[PATCH -tip v2 0/3] x86/callthunks: Fix and unify call thunk assembly snippets

[PATCH -tip v2 0/3] x86/callthunks: Fix and unify call thunk assembly snippets

[Uros Bizjak]

Currently INCREMENT_CALL_DEPTH and thunk debug macros explicitly
define %gs: segment register prefix for their percpu variables.
This is not compatible with !CONFIG_SMP, which requires non-prefixed
percpu variables.

Contrary to alternatives, relocations are currently not supported in
call thunk templates.  Due to unsupported relocations, two variants of
INCREMENT_CALL_DEPTH macro are needed, ASM_ prefixed that allows
relocations and non-prefixed version that allows only absolute
addresses.

The following patch series fixes above issues by

a) Making PER_CPU_VAR macro from percpu.h also available without
__ASSEMBLY__, so it can be used in 'asm' statements to conditionally
use %gs: segment register prefix, depending on CONFIG_SMP.

b) Re-using existing infrastructure from alternative.c to allow
%rip-relative relocations when copying call thunk template from its
storage location.

c) Fixing call thunks debug macros to use PER_CPU_VAR macro from
percpu.h to conditionally use %gs: segment register prefix, depending
on CONFIG_SMP.

d) Unifying ASM_ prefixed assembly macros with their non-prefixed
variants. With support of %rip-relative relocations in place, call
thunk templates allow %rip-relative addressing, so unified assembly
snippet can be used everywhere.

v2:
- Make PER_CPU_VAR macro available in 'asm' statements instead of
  moving 'asm' statements to *.S assembly files.
- Re-use existing relocation infrastructure from alternative.c

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>

Uros Bizjak (3):
  x86/percpu: Define PER_CPU_VAR macro also for !__ASSEMBLY__
  x86/callthunks: Handle %rip-relative relocations in call thunk
    template
  x86/callthunks: Fix and unify call thunks assembly snippets

 arch/x86/include/asm/nospec-branch.h | 23 ++++++--------------
 arch/x86/include/asm/percpu.h        |  5 +++++
 arch/x86/include/asm/text-patching.h |  2 ++
 arch/x86/kernel/alternative.c        |  3 +--
 arch/x86/kernel/callthunks.c         | 32 ++++++++++++++++++++++------
 5 files changed, 40 insertions(+), 25 deletions(-)

-- 
2.41.0

[PATCH -tip v2 1/3] x86/percpu: Define PER_CPU_VAR macro also for !__ASSEMBLY__

[Uros Bizjak]

Some C source files define 'asm' statements that use PER_CPU_VAR,
so make PER_CPU_VAR macro available also without __ASSEMBLY__.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
v2: Make PER_CPU_VAR macro available in 'asm' statements
    instead of moving 'asm' statements to *.S assembly files.
---
 arch/x86/include/asm/percpu.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index b86b27d15e52..0f12b2004b94 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -84,10 +84,15 @@
 })
 #endif /* CONFIG_USE_X86_SEG_SUPPORT */
 
+#define PER_CPU_VAR(var)	%__percpu_seg:(var)__percpu_rel
+
 #else /* CONFIG_SMP */
 #define __percpu_seg_override
 #define __percpu_prefix		""
 #define __force_percpu_prefix	""
+
+#define PER_CPU_VAR(var)	(var)__percpu_rel
+
 #endif /* CONFIG_SMP */
 
 #define __my_cpu_type(var)	typeof(var) __percpu_seg_override
-- 
2.41.0

[tip: x86/percpu] x86/percpu: Define PER_CPU_VAR macro also for !__ASSEMBLY__

[tip-bot2 for Uros Bizjak]

The following commit has been merged into the x86/percpu branch of tip:

Commit-ID:     43bda69ed9e3b86d0ba5ff9256e437d50074d7d5
Gitweb:        https://git.kernel.org/tip/43bda69ed9e3b86d0ba5ff9256e437d50074d7d5
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Sun, 05 Nov 2023 22:34:35 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Thu, 30 Nov 2023 20:06:16 +01:00

x86/percpu: Define PER_CPU_VAR macro also for !__ASSEMBLY__

Some C source files define 'asm' statements that use PER_CPU_VAR,
so make PER_CPU_VAR macro available also without __ASSEMBLY__.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231105213731.1878100-2-ubizjak@gmail.com
---
 arch/x86/include/asm/percpu.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index b86b27d..0f12b20 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -84,10 +84,15 @@
 })
 #endif /* CONFIG_USE_X86_SEG_SUPPORT */
 
+#define PER_CPU_VAR(var)	%__percpu_seg:(var)__percpu_rel
+
 #else /* CONFIG_SMP */
 #define __percpu_seg_override
 #define __percpu_prefix		""
 #define __force_percpu_prefix	""
+
+#define PER_CPU_VAR(var)	(var)__percpu_rel
+
 #endif /* CONFIG_SMP */
 
 #define __my_cpu_type(var)	typeof(var) __percpu_seg_override

[PATCH -tip v2 2/3] x86/callthunks: Handle %rip-relative relocations in call thunk template

[Uros Bizjak]

Contrary to alternatives, relocations are currently not supported in
call thunk templates.  Re-use the existing infrastructure from
alternative.c to allow %rip-relative relocations when copying call
thunk template from its storage location.

The patch allows unification of ASM_INCREMENT_CALL_DEPTH, which already
uses PER_CPU_VAR macro, with INCREMENT_CALL_DEPTH, used in call thunk
template, which is currently limited to use absolute address.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
v2: Reuse existing relocation infrastructure from alternative.c.
---
 arch/x86/include/asm/text-patching.h |  2 ++
 arch/x86/kernel/alternative.c        |  3 +--
 arch/x86/kernel/callthunks.c         | 32 ++++++++++++++++++++++------
 3 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index 29832c338cdc..ba8d900f3ebe 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -18,6 +18,8 @@ static inline void apply_paravirt(struct paravirt_patch_site *start,
 #define __parainstructions_end	NULL
 #endif
 
+void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len);
+
 /*
  * Currently, the max observed size in the kernel code is
  * JUMP_LABEL_NOP_SIZE/RELATIVEJUMP_SIZE, which are 5.
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 73be3931e4f0..66140c54d4f6 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -325,8 +325,7 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
 	return (target < src || target > src + src_len);
 }
 
-static void __init_or_module noinline
-apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
+void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 {
 	int prev, target = 0;
 
diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index e9ad518a5003..ef9c04707b3c 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -24,6 +24,8 @@
 
 static int __initdata_or_module debug_callthunks;
 
+#define MAX_PATCH_LEN (255-1)
+
 #define prdbg(fmt, args...)					\
 do {								\
 	if (debug_callthunks)					\
@@ -179,10 +181,15 @@ static const u8 nops[] = {
 static void *patch_dest(void *dest, bool direct)
 {
 	unsigned int tsize = SKL_TMPL_SIZE;
+	u8 insn_buff[MAX_PATCH_LEN];
 	u8 *pad = dest - tsize;
 
+	memcpy(insn_buff, skl_call_thunk_template, tsize);
+	apply_relocation(insn_buff, tsize, pad,
+			 skl_call_thunk_template, tsize);
+
 	/* Already patched? */
-	if (!bcmp(pad, skl_call_thunk_template, tsize))
+	if (!bcmp(pad, insn_buff, tsize))
 		return pad;
 
 	/* Ensure there are nops */
@@ -192,9 +199,9 @@ static void *patch_dest(void *dest, bool direct)
 	}
 
 	if (direct)
-		memcpy(pad, skl_call_thunk_template, tsize);
+		memcpy(pad, insn_buff, tsize);
 	else
-		text_poke_copy_locked(pad, skl_call_thunk_template, tsize, true);
+		text_poke_copy_locked(pad, insn_buff, tsize, true);
 	return pad;
 }
 
@@ -291,20 +298,27 @@ void *callthunks_translate_call_dest(void *dest)
 static bool is_callthunk(void *addr)
 {
 	unsigned int tmpl_size = SKL_TMPL_SIZE;
-	void *tmpl = skl_call_thunk_template;
+	u8 insn_buff[MAX_PATCH_LEN];
 	unsigned long dest;
+	u8 *pad;
 
 	dest = roundup((unsigned long)addr, CONFIG_FUNCTION_ALIGNMENT);
 	if (!thunks_initialized || skip_addr((void *)dest))
 		return false;
 
-	return !bcmp((void *)(dest - tmpl_size), tmpl, tmpl_size);
+	*pad = dest - tmpl_size;
+
+	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
+	apply_relocation(insn_buff, tmpl_size, pad,
+			 skl_call_thunk_template, tmpl_size);
+
+	return !bcmp(pad, insn_buff, tmpl_size);
 }
 
 int x86_call_depth_emit_accounting(u8 **pprog, void *func)
 {
 	unsigned int tmpl_size = SKL_TMPL_SIZE;
-	void *tmpl = skl_call_thunk_template;
+	u8 insn_buff[MAX_PATCH_LEN];
 
 	if (!thunks_initialized)
 		return 0;
@@ -313,7 +327,11 @@ int x86_call_depth_emit_accounting(u8 **pprog, void *func)
 	if (func && is_callthunk(func))
 		return 0;
 
-	memcpy(*pprog, tmpl, tmpl_size);
+	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
+	apply_relocation(insn_buff, tmpl_size, *pprog,
+			 skl_call_thunk_template, tmpl_size);
+
+	memcpy(*pprog, insn_buff, tmpl_size);
 	*pprog += tmpl_size;
 	return tmpl_size;
 }
-- 
2.41.0

[tip: x86/percpu] x86/callthunks: Mark apply_relocation() as __init_or_module

[tip-bot2 for Ingo Molnar]

The following commit has been merged into the x86/percpu branch of tip:

Commit-ID:     6724ba89e0b03667d56616614f55e1f772d38fdb
Gitweb:        https://git.kernel.org/tip/6724ba89e0b03667d56616614f55e1f772d38fdb
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Thu, 30 Nov 2023 20:15:51 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Thu, 30 Nov 2023 20:15:51 +01:00

x86/callthunks: Mark apply_relocation() as __init_or_module

Do it like the rest of the methods using it.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20231105213731.1878100-3-ubizjak@gmail.com
---
 arch/x86/include/asm/text-patching.h | 2 +-
 arch/x86/kernel/alternative.c        | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index ba8d900..fb338f0 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -18,7 +18,7 @@ static inline void apply_paravirt(struct paravirt_patch_site *start,
 #define __parainstructions_end	NULL
 #endif
 
-void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len);
+extern void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len);
 
 /*
  * Currently, the max observed size in the kernel code is
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index aa86415..5052371 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -325,7 +325,7 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
 	return (target < src || target > src + src_len);
 }
 
-void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
+void __init_or_module apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 {
 	int prev, target = 0;
 

Re: [tip: x86/percpu] x86/callthunks: Mark apply_relocation() as __init_or_module

[Borislav Petkov]

On Thu, Nov 30, 2023 at 09:16:31PM -0000, tip-bot2 for Ingo Molnar wrote:
> -void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
> +void __init_or_module apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
>  {
>  	int prev, target = 0;

Can't do that for a CONFIG_MODULES=n build:

WARNING: modpost: vmlinux: section mismatch in reference: patch_dest+0x61 (section: .text) -> apply_relocation (section: .init.text)
ERROR: modpost: Section mismatches detected.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

[tip: x86/percpu] x86/callthunks: Handle %rip-relative relocations in call thunk template

[tip-bot2 for Uros Bizjak]

The following commit has been merged into the x86/percpu branch of tip:

Commit-ID:     17bce3b2ae2d52e8c5c12274ce4c3a631ce9e66b
Gitweb:        https://git.kernel.org/tip/17bce3b2ae2d52e8c5c12274ce4c3a631ce9e66b
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Sun, 05 Nov 2023 22:34:36 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Thu, 30 Nov 2023 20:06:17 +01:00

x86/callthunks: Handle %rip-relative relocations in call thunk template

Contrary to alternatives, relocations are currently not supported in
call thunk templates.  Re-use the existing infrastructure from
alternative.c to allow %rip-relative relocations when copying call
thunk template from its storage location.

The patch allows unification of ASM_INCREMENT_CALL_DEPTH, which already
uses PER_CPU_VAR macro, with INCREMENT_CALL_DEPTH, used in call thunk
template, which is currently limited to use absolute address.

Reuse existing relocation infrastructure from alternative.c.,
as suggested by Peter Zijlstra.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231105213731.1878100-3-ubizjak@gmail.com
---
 arch/x86/include/asm/text-patching.h |  2 ++-
 arch/x86/kernel/alternative.c        |  3 +--
 arch/x86/kernel/callthunks.c         | 32 +++++++++++++++++++++------
 3 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index 29832c3..ba8d900 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -18,6 +18,8 @@ static inline void apply_paravirt(struct paravirt_patch_site *start,
 #define __parainstructions_end	NULL
 #endif
 
+void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len);
+
 /*
  * Currently, the max observed size in the kernel code is
  * JUMP_LABEL_NOP_SIZE/RELATIVEJUMP_SIZE, which are 5.
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index a5ead6a..aa86415 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -325,8 +325,7 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
 	return (target < src || target > src + src_len);
 }
 
-static void __init_or_module noinline
-apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
+void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 {
 	int prev, target = 0;
 
diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index c06bfc0..f56fa30 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -24,6 +24,8 @@
 
 static int __initdata_or_module debug_callthunks;
 
+#define MAX_PATCH_LEN (255-1)
+
 #define prdbg(fmt, args...)					\
 do {								\
 	if (debug_callthunks)					\
@@ -184,10 +186,15 @@ static const u8 nops[] = {
 static void *patch_dest(void *dest, bool direct)
 {
 	unsigned int tsize = SKL_TMPL_SIZE;
+	u8 insn_buff[MAX_PATCH_LEN];
 	u8 *pad = dest - tsize;
 
+	memcpy(insn_buff, skl_call_thunk_template, tsize);
+	apply_relocation(insn_buff, tsize, pad,
+			 skl_call_thunk_template, tsize);
+
 	/* Already patched? */
-	if (!bcmp(pad, skl_call_thunk_template, tsize))
+	if (!bcmp(pad, insn_buff, tsize))
 		return pad;
 
 	/* Ensure there are nops */
@@ -197,9 +204,9 @@ static void *patch_dest(void *dest, bool direct)
 	}
 
 	if (direct)
-		memcpy(pad, skl_call_thunk_template, tsize);
+		memcpy(pad, insn_buff, tsize);
 	else
-		text_poke_copy_locked(pad, skl_call_thunk_template, tsize, true);
+		text_poke_copy_locked(pad, insn_buff, tsize, true);
 	return pad;
 }
 
@@ -297,20 +304,27 @@ void *callthunks_translate_call_dest(void *dest)
 static bool is_callthunk(void *addr)
 {
 	unsigned int tmpl_size = SKL_TMPL_SIZE;
-	void *tmpl = skl_call_thunk_template;
+	u8 insn_buff[MAX_PATCH_LEN];
 	unsigned long dest;
+	u8 *pad;
 
 	dest = roundup((unsigned long)addr, CONFIG_FUNCTION_ALIGNMENT);
 	if (!thunks_initialized || skip_addr((void *)dest))
 		return false;
 
-	return !bcmp((void *)(dest - tmpl_size), tmpl, tmpl_size);
+	*pad = dest - tmpl_size;
+
+	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
+	apply_relocation(insn_buff, tmpl_size, pad,
+			 skl_call_thunk_template, tmpl_size);
+
+	return !bcmp(pad, insn_buff, tmpl_size);
 }
 
 int x86_call_depth_emit_accounting(u8 **pprog, void *func)
 {
 	unsigned int tmpl_size = SKL_TMPL_SIZE;
-	void *tmpl = skl_call_thunk_template;
+	u8 insn_buff[MAX_PATCH_LEN];
 
 	if (!thunks_initialized)
 		return 0;
@@ -319,7 +333,11 @@ int x86_call_depth_emit_accounting(u8 **pprog, void *func)
 	if (func && is_callthunk(func))
 		return 0;
 
-	memcpy(*pprog, tmpl, tmpl_size);
+	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
+	apply_relocation(insn_buff, tmpl_size, *pprog,
+			 skl_call_thunk_template, tmpl_size);
+
+	memcpy(*pprog, insn_buff, tmpl_size);
 	*pprog += tmpl_size;
 	return tmpl_size;
 }

Re: [PATCH -tip v2 2/3] x86/callthunks: Handle %rip-relative relocations in call thunk template

[Nathan Chancellor]

Hi Uros,

On Sun, Nov 05, 2023 at 10:34:36PM +0100, Uros Bizjak wrote:
> Contrary to alternatives, relocations are currently not supported in
> call thunk templates.  Re-use the existing infrastructure from
> alternative.c to allow %rip-relative relocations when copying call
> thunk template from its storage location.
> 
> The patch allows unification of ASM_INCREMENT_CALL_DEPTH, which already
> uses PER_CPU_VAR macro, with INCREMENT_CALL_DEPTH, used in call thunk
> template, which is currently limited to use absolute address.
> 
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
...
> diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
> index e9ad518a5003..ef9c04707b3c 100644
> --- a/arch/x86/kernel/callthunks.c
> +++ b/arch/x86/kernel/callthunks.c
...
> @@ -291,20 +298,27 @@ void *callthunks_translate_call_dest(void *dest)
>  static bool is_callthunk(void *addr)
>  {
>  	unsigned int tmpl_size = SKL_TMPL_SIZE;
> -	void *tmpl = skl_call_thunk_template;
> +	u8 insn_buff[MAX_PATCH_LEN];
>  	unsigned long dest;
> +	u8 *pad;
>  
>  	dest = roundup((unsigned long)addr, CONFIG_FUNCTION_ALIGNMENT);
>  	if (!thunks_initialized || skip_addr((void *)dest))
>  		return false;
>  
> -	return !bcmp((void *)(dest - tmpl_size), tmpl, tmpl_size);
> +	*pad = dest - tmpl_size;

Clang warns (or errors with CONFIG_WERROR=y):

  arch/x86/kernel/callthunks.c:315:3: error: variable 'pad' is uninitialized when used here [-Werror,-Wuninitialized]
    315 |         *pad = dest - tmpl_size;
        |          ^~~
  arch/x86/kernel/callthunks.c:309:9: note: initialize the variable 'pad' to silence this warning
    309 |         u8 *pad;
        |                ^
        |                 = NULL
  1 error generated.

which came from our continuous integration:

https://github.com/ClangBuiltLinux/continuous-integration2/actions/runs/7054081453/job/19205345548
https://storage.tuxsuite.com/public/clangbuiltlinux/continuous-integration2/builds/2Yv1FATZZIeD3P7S57ZkHYhyZ8A/build.log

> +
> +	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
> +	apply_relocation(insn_buff, tmpl_size, pad,
> +			 skl_call_thunk_template, tmpl_size);
> +
> +	return !bcmp(pad, insn_buff, tmpl_size);
>  }

Cheers,
Nathan

Re: [PATCH -tip v2 2/3] x86/callthunks: Handle %rip-relative relocations in call thunk template

[Uros Bizjak]

[-- Attachment #1: Type: text/plain, Size: 2069 bytes --]

On Fri, Dec 1, 2023 at 4:55 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Hi Uros,
>
> On Sun, Nov 05, 2023 at 10:34:36PM +0100, Uros Bizjak wrote:
> > Contrary to alternatives, relocations are currently not supported in
> > call thunk templates.  Re-use the existing infrastructure from
> > alternative.c to allow %rip-relative relocations when copying call
> > thunk template from its storage location.
> >
> > The patch allows unification of ASM_INCREMENT_CALL_DEPTH, which already
> > uses PER_CPU_VAR macro, with INCREMENT_CALL_DEPTH, used in call thunk
> > template, which is currently limited to use absolute address.
> >
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Borislav Petkov <bp@alien8.de>
> > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> ...
> > diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
> > index e9ad518a5003..ef9c04707b3c 100644
> > --- a/arch/x86/kernel/callthunks.c
> > +++ b/arch/x86/kernel/callthunks.c
> ...
> > @@ -291,20 +298,27 @@ void *callthunks_translate_call_dest(void *dest)
> >  static bool is_callthunk(void *addr)
> >  {
> >       unsigned int tmpl_size = SKL_TMPL_SIZE;
> > -     void *tmpl = skl_call_thunk_template;
> > +     u8 insn_buff[MAX_PATCH_LEN];
> >       unsigned long dest;
> > +     u8 *pad;
> >
> >       dest = roundup((unsigned long)addr, CONFIG_FUNCTION_ALIGNMENT);
> >       if (!thunks_initialized || skip_addr((void *)dest))
> >               return false;
> >
> > -     return !bcmp((void *)(dest - tmpl_size), tmpl, tmpl_size);
> > +     *pad = dest - tmpl_size;
>
> Clang warns (or errors with CONFIG_WERROR=y):

Uh, GCC didn't warn at all (and there is some mixup with types here,
so a thinko slipped through.

The attached patch fixes the oversight. I'll post a formal patch later
today after some more testing.

Thanks,
Uros.

[-- Attachment #2: p.diff.txt --]
[-- Type: text/plain, Size: 479 bytes --]

diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index f5507c95e7be..71b74a07c8ee 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -306,7 +306,7 @@ static bool is_callthunk(void *addr)
 	if (!thunks_initialized || skip_addr((void *)dest))
 		return false;
 
-	*pad = dest - tmpl_size;
+	pad = (void *)dest - tmpl_size;
 
 	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
 	apply_relocation(insn_buff, tmpl_size, pad,

[PATCH -tip v2 3/3] x86/callthunks: Fix and unify call thunks assembly snippets

[Uros Bizjak]

Currently thunk debug macros explicitly define %gs: segment register
prefix for their percpu variables. This is not compatible with
!CONFIG_SMP, which requires non-prefixed percpu variables.

Fix call thunks debug macros to use PER_CPU_VAR macro from percpu.h
to conditionally use %gs: segment register prefix, depending on
CONFIG_SMP.

Finally, unify ASM_ prefixed assembly macros with their non-prefixed
variants. With support of %rip-relative relocations in place, call
thunk templates allow %rip-relative addressing, so unified assembly
snippet can be used everywhere.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
 arch/x86/include/asm/nospec-branch.h | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index f93e9b96927a..6f677be6bdb9 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -59,13 +59,13 @@
 
 #ifdef CONFIG_CALL_THUNKS_DEBUG
 # define CALL_THUNKS_DEBUG_INC_CALLS				\
-	incq	%gs:__x86_call_count;
+	incq	PER_CPU_VAR(__x86_call_count);
 # define CALL_THUNKS_DEBUG_INC_RETS				\
-	incq	%gs:__x86_ret_count;
+	incq	PER_CPU_VAR(__x86_ret_count);
 # define CALL_THUNKS_DEBUG_INC_STUFFS				\
-	incq	%gs:__x86_stuffs_count;
+	incq	PER_CPU_VAR(__x86_stuffs_count);
 # define CALL_THUNKS_DEBUG_INC_CTXSW				\
-	incq	%gs:__x86_ctxsw_count;
+	incq	PER_CPU_VAR(__x86_ctxsw_count);
 #else
 # define CALL_THUNKS_DEBUG_INC_CALLS
 # define CALL_THUNKS_DEBUG_INC_RETS
@@ -80,9 +80,6 @@
 #define CREDIT_CALL_DEPTH					\
 	movq	$-1, PER_CPU_VAR(pcpu_hot + X86_call_depth);
 
-#define ASM_CREDIT_CALL_DEPTH					\
-	movq	$-1, PER_CPU_VAR(pcpu_hot + X86_call_depth);
-
 #define RESET_CALL_DEPTH					\
 	xor	%eax, %eax;					\
 	bts	$63, %rax;					\
@@ -95,20 +92,14 @@
 	CALL_THUNKS_DEBUG_INC_CALLS
 
 #define INCREMENT_CALL_DEPTH					\
-	sarq	$5, %gs:pcpu_hot + X86_call_depth;		\
-	CALL_THUNKS_DEBUG_INC_CALLS
-
-#define ASM_INCREMENT_CALL_DEPTH				\
 	sarq	$5, PER_CPU_VAR(pcpu_hot + X86_call_depth);	\
 	CALL_THUNKS_DEBUG_INC_CALLS
 
 #else
 #define CREDIT_CALL_DEPTH
-#define ASM_CREDIT_CALL_DEPTH
 #define RESET_CALL_DEPTH
-#define INCREMENT_CALL_DEPTH
-#define ASM_INCREMENT_CALL_DEPTH
 #define RESET_CALL_DEPTH_FROM_CALL
+#define INCREMENT_CALL_DEPTH
 #endif
 
 /*
@@ -158,7 +149,7 @@
 	jnz	771b;					\
 	/* barrier for jnz misprediction */		\
 	lfence;						\
-	ASM_CREDIT_CALL_DEPTH				\
+	CREDIT_CALL_DEPTH				\
 	CALL_THUNKS_DEBUG_INC_CTXSW
 #else
 /*
@@ -311,7 +302,7 @@
 .macro CALL_DEPTH_ACCOUNT
 #ifdef CONFIG_CALL_DEPTH_TRACKING
 	ALTERNATIVE "",							\
-		    __stringify(ASM_INCREMENT_CALL_DEPTH), X86_FEATURE_CALL_DEPTH
+		    __stringify(INCREMENT_CALL_DEPTH), X86_FEATURE_CALL_DEPTH
 #endif
 .endm
 
-- 
2.41.0

[tip: x86/percpu] x86/callthunks: Fix and unify call thunks assembly snippets

[tip-bot2 for Uros Bizjak]

The following commit has been merged into the x86/percpu branch of tip:

Commit-ID:     2adeed985a42ff3334e6898c8c0827e7626c1336
Gitweb:        https://git.kernel.org/tip/2adeed985a42ff3334e6898c8c0827e7626c1336
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Sun, 05 Nov 2023 22:34:37 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Thu, 30 Nov 2023 20:06:17 +01:00

x86/callthunks: Fix and unify call thunks assembly snippets

Currently thunk debug macros explicitly define %gs: segment register
prefix for their percpu variables. This is not compatible with
!CONFIG_SMP, which requires non-prefixed percpu variables.

Fix call thunks debug macros to use PER_CPU_VAR macro from percpu.h
to conditionally use %gs: segment register prefix, depending on
CONFIG_SMP.

Finally, unify ASM_ prefixed assembly macros with their non-prefixed
variants. With support of %rip-relative relocations in place, call
thunk templates allow %rip-relative addressing, so unified assembly
snippet can be used everywhere.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231105213731.1878100-4-ubizjak@gmail.com
---
 arch/x86/include/asm/nospec-branch.h | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index c55cc24..65fbf6b 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -59,13 +59,13 @@
 
 #ifdef CONFIG_CALL_THUNKS_DEBUG
 # define CALL_THUNKS_DEBUG_INC_CALLS				\
-	incq	%gs:__x86_call_count;
+	incq	PER_CPU_VAR(__x86_call_count);
 # define CALL_THUNKS_DEBUG_INC_RETS				\
-	incq	%gs:__x86_ret_count;
+	incq	PER_CPU_VAR(__x86_ret_count);
 # define CALL_THUNKS_DEBUG_INC_STUFFS				\
-	incq	%gs:__x86_stuffs_count;
+	incq	PER_CPU_VAR(__x86_stuffs_count);
 # define CALL_THUNKS_DEBUG_INC_CTXSW				\
-	incq	%gs:__x86_ctxsw_count;
+	incq	PER_CPU_VAR(__x86_ctxsw_count);
 #else
 # define CALL_THUNKS_DEBUG_INC_CALLS
 # define CALL_THUNKS_DEBUG_INC_RETS
@@ -80,9 +80,6 @@
 #define CREDIT_CALL_DEPTH					\
 	movq	$-1, PER_CPU_VAR(pcpu_hot + X86_call_depth);
 
-#define ASM_CREDIT_CALL_DEPTH					\
-	movq	$-1, PER_CPU_VAR(pcpu_hot + X86_call_depth);
-
 #define RESET_CALL_DEPTH					\
 	xor	%eax, %eax;					\
 	bts	$63, %rax;					\
@@ -95,20 +92,14 @@
 	CALL_THUNKS_DEBUG_INC_CALLS
 
 #define INCREMENT_CALL_DEPTH					\
-	sarq	$5, %gs:pcpu_hot + X86_call_depth;		\
-	CALL_THUNKS_DEBUG_INC_CALLS
-
-#define ASM_INCREMENT_CALL_DEPTH				\
 	sarq	$5, PER_CPU_VAR(pcpu_hot + X86_call_depth);	\
 	CALL_THUNKS_DEBUG_INC_CALLS
 
 #else
 #define CREDIT_CALL_DEPTH
-#define ASM_CREDIT_CALL_DEPTH
 #define RESET_CALL_DEPTH
-#define INCREMENT_CALL_DEPTH
-#define ASM_INCREMENT_CALL_DEPTH
 #define RESET_CALL_DEPTH_FROM_CALL
+#define INCREMENT_CALL_DEPTH
 #endif
 
 /*
@@ -158,7 +149,7 @@
 	jnz	771b;					\
 	/* barrier for jnz misprediction */		\
 	lfence;						\
-	ASM_CREDIT_CALL_DEPTH				\
+	CREDIT_CALL_DEPTH				\
 	CALL_THUNKS_DEBUG_INC_CTXSW
 #else
 /*
@@ -325,7 +316,7 @@
 .macro CALL_DEPTH_ACCOUNT
 #ifdef CONFIG_CALL_DEPTH_TRACKING
 	ALTERNATIVE "",							\
-		    __stringify(ASM_INCREMENT_CALL_DEPTH), X86_FEATURE_CALL_DEPTH
+		    __stringify(INCREMENT_CALL_DEPTH), X86_FEATURE_CALL_DEPTH
 #endif
 .endm