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* [PATCH 0/3] x86/cfi: Fix a few kCFI issues found with GCC
@ 2026-10-12  9:04 Kees Cook
  2026-10-12  9:04 ` [PATCH 1/3] x86/kcfi: Decode the kCFI check from the trap address Kees Cook
                   ` (2 more replies)
  0 siblings, 3 replies; 8+ messages in thread
From: Kees Cook @ 2026-10-12  9:04 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Kees Cook, Josh Poimboeuf, Thomas Gleixner, Ingo Molnar,
	Borislav Petkov, Dave Hansen, H. Peter Anvin, Sami Tolvanen,
	Nathan Chancellor, Nick Desaulniers, Bill Wendling, Justin Stitt,
	x86, llvm, linux-kernel, linux-hardening

Hi!

While testing x86 kernels built by GCC with the coming kCFI patches I
tripped over three problems. Since the kCFI call sequence was optimized
in v7.3-rc1, the trap handler decodes the check one byte off, so a
kCFI failure in a CONFIG_FINEIBT=y kernel running in kCFI mode reports
whatever %rbx holds as the target, with Clang as well as GCC (1/3). GNU
as warns about the "cs" prefix in the FineIBT paranoid caller template,
which Clang's integrated assembler accepts silently (2/3). And objtool's
kCFI check treats GCC's jump-table jump for the BPF interpreter's computed
goto as an unchecked indirect call (3/3).

Thanks!

-Kees

Kees Cook (3):
  x86/kcfi: Decode the kCFI check from the trap address
  x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte
  objtool: Skip jump table jumps in the kCFI indirect call check

 arch/x86/kernel/alternative.c |  3 ++-
 arch/x86/kernel/cfi.c         | 14 +++++++-------
 tools/objtool/check.c         |  8 ++++++++
 3 files changed, 17 insertions(+), 8 deletions(-)

-- 
2.55.0


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [PATCH 1/3] x86/kcfi: Decode the kCFI check from the trap address
  2026-10-12  9:04 [PATCH 0/3] x86/cfi: Fix a few kCFI issues found with GCC Kees Cook
@ 2026-10-12  9:04 ` Kees Cook
  2026-10-12  9:59   ` [tip: x86/urgent] " tip-bot2 for Kees Cook
  2026-10-12  9:04 ` [PATCH 2/3] x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte Kees Cook
  2026-10-12  9:04 ` [PATCH 3/3] objtool: Skip jump table jumps in the kCFI indirect call check Kees Cook
  2 siblings, 1 reply; 8+ messages in thread
From: Kees Cook @ 2026-10-12  9:04 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Kees Cook, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
	Dave Hansen, H. Peter Anvin, Sami Tolvanen, Nathan Chancellor,
	Nick Desaulniers, Bill Wendling, Justin Stitt, x86, llvm,
	linux-kernel, linux-hardening

Since commit b2250d63e6422 ("x86/kcfi: Optimize call sequence"), a
CONFIG_FINEIBT=y kernel running in kCFI mode rewrites each kCFI call
site at boot so that a failed check traps on the 0xd6 byte of
"test $0xd6, %al", one byte past where the compiler's "ud2" was.
handle_cfi_failure() steps "addr" back one byte to find the trap in
.kcfi_traps, but decode_cfi_insn() still decodes from regs->ip, so it
reads each instruction starting at its second byte.
"movl $-<id>, %r10d" then decodes as "movl $-<id>, %edx", so the
reported type is right by accident, but "addl -15(%r11), %r10d" decodes
as "addl -15(%rbx), %edx", so the reported target is whatever %rbx holds:

  CFI failure at lkdtm_indirect_call+0x16/0x20 (target: 0x12; expected type: 0xc79a2d1b)

Pass the adjusted address to decode_cfi_insn() and decode from it.

Tested ARCH=x86_64 defconfig with CONFIG_CFI=y and CONFIG_LKDTM=y under
QEMU, with LKDTM's CFI_FORWARD_PROTO and both Clang 24.0.0git and GCC
17.0.0 (experimental, with the kCFI series). With CONFIG_FINEIBT=y in
kCFI mode, the report gives %rbx as the target without this change, and
the expected lkdtm_increment_int() with it. With cfi=fineibt, with
cfi=fineibt,paranoid, and with CONFIG_FINEIBT=n, it gives
lkdtm_increment_int() both with and without this change.

Fixes: b2250d63e6422 ("x86/kcfi: Optimize call sequence")
Assisted-by: LLM
Signed-off-by: Kees Cook <kees@kernel.org>
---
 arch/x86/kernel/cfi.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cfi.c b/arch/x86/kernel/cfi.c
index 1df26dfdce08..8e5c4ed264a0 100644
--- a/arch/x86/kernel/cfi.c
+++ b/arch/x86/kernel/cfi.c
@@ -10,11 +10,11 @@
 #include <asm/insn-eval.h>
 
 /*
- * Returns the target address and the expected type when regs->ip points
+ * Returns the target address and the expected type when addr points
  * to a compiler-generated CFI trap.
  */
-static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
-			    u32 *type)
+static bool decode_cfi_insn(struct pt_regs *regs, unsigned long addr,
+			    unsigned long *target, u32 *type)
 {
 	char buffer[MAX_INSN_SIZE];
 	struct insn insn;
@@ -29,13 +29,13 @@ static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
 	 *   movl    -<id>, %r10d       ; 6 bytes
 	 *   addl    -<pos>(%reg), %r10d; 4 bytes
 	 *   je      .Ltmp1             ; 2 bytes
-	 *   ud2                        ; <- regs->ip
+	 *   ud2                        ; <- addr
 	 *   .Ltmp1:
 	 *
 	 * We can decode the expected type and the target address from the
 	 * movl/addl instructions.
 	 */
-	if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 12, MAX_INSN_SIZE))
+	if (copy_from_kernel_nofault(buffer, (void *)addr - 12, MAX_INSN_SIZE))
 		return false;
 	if (insn_decode_kernel(&insn, &buffer[offset]))
 		return false;
@@ -44,7 +44,7 @@ static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
 
 	*type = -(u32)insn.immediate.value;
 
-	if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 6, MAX_INSN_SIZE))
+	if (copy_from_kernel_nofault(buffer, (void *)addr - 6, MAX_INSN_SIZE))
 		return false;
 	if (insn_decode_kernel(&insn, &buffer[offset]))
 		return false;
@@ -82,7 +82,7 @@ enum bug_trap_type handle_cfi_failure(struct pt_regs *regs)
 				return BUG_TRAP_TYPE_NONE;
 		}
 
-		if (!decode_cfi_insn(regs, &target, &type))
+		if (!decode_cfi_insn(regs, addr, &target, &type))
 			return report_cfi_failure_noaddr(regs, addr);
 
 		break;
-- 
2.55.0


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [PATCH 2/3] x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte
  2026-10-12  9:04 [PATCH 0/3] x86/cfi: Fix a few kCFI issues found with GCC Kees Cook
  2026-10-12  9:04 ` [PATCH 1/3] x86/kcfi: Decode the kCFI check from the trap address Kees Cook
@ 2026-10-12  9:04 ` Kees Cook
  2026-10-12  9:16   ` Peter Zijlstra
  2026-10-12  9:59   ` [tip: x86/core] " tip-bot2 for Kees Cook
  2026-10-12  9:04 ` [PATCH 3/3] objtool: Skip jump table jumps in the kCFI indirect call check Kees Cook
  2 siblings, 2 replies; 8+ messages in thread
From: Kees Cook @ 2026-10-12  9:04 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Kees Cook, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
	Dave Hansen, H. Peter Anvin, Sami Tolvanen, Nathan Chancellor,
	Nick Desaulniers, Bill Wendling, Justin Stitt, x86, llvm,
	linux-kernel, linux-hardening

The "cs" prefix on the LEA in the FineIBT paranoid caller template is
padding: it places the LEA's 0xf0 immediate byte where it doubles as the
LOCK prefix that makes the failing Jcc raise #UD. GNU as warns about it
in every CONFIG_FINEIBT=y build:

  Warning: segment override on `lea' is ineffectual

Clang's integrated assembler does not warn, and both assemble the same
bytes. Emit the prefix with ".byte 0x2e" to silence GNU as.

Build tested ARCH=x86_64 defconfig with CONFIG_CFI=y, with GCC 17.0.0
(experimental, with the kCFI series) and GNU as 2.47, and with Clang
24.0.0git: GNU as no longer warns, and the template assembles to the
same bytes as before with both. Under QEMU with cfi=fineibt,paranoid,
the paranoid caller check catches LKDTM's CFI_FORWARD_PROTO with both.

Assisted-by: LLM
Signed-off-by: Kees Cook <kees@kernel.org>
---
 arch/x86/kernel/alternative.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 91b1cdd16569..1300ca50e770 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1448,7 +1448,8 @@ asm(	".pushsection .rodata				\n"
 	"fineibt_paranoid_start:			\n"
 	"	mov	$0x12345678, %eax		\n"
 	"	cmpl	-11(%r11), %eax			\n"
-	"	cs lea	-0x10(%r11), %r11		\n"
+	"	.byte	0x2e				\n"
+	"	lea	-0x10(%r11), %r11		\n"
 	"#fineibt_caller_size:                          \n"
 	"	jne	fineibt_paranoid_start+0xd	\n"
 	"fineibt_paranoid_ind:				\n"
-- 
2.55.0


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [PATCH 3/3] objtool: Skip jump table jumps in the kCFI indirect call check
  2026-10-12  9:04 [PATCH 0/3] x86/cfi: Fix a few kCFI issues found with GCC Kees Cook
  2026-10-12  9:04 ` [PATCH 1/3] x86/kcfi: Decode the kCFI check from the trap address Kees Cook
  2026-10-12  9:04 ` [PATCH 2/3] x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte Kees Cook
@ 2026-10-12  9:04 ` Kees Cook
  2026-10-12  9:22   ` Peter Zijlstra
  2 siblings, 1 reply; 8+ messages in thread
From: Kees Cook @ 2026-10-12  9:04 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Kees Cook, Josh Poimboeuf, Sami Tolvanen, Nathan Chancellor,
	Nick Desaulniers, Bill Wendling, Justin Stitt, llvm,
	linux-kernel, linux-hardening

With MITIGATION_RETPOLINE=y, GCC lowers the computed goto in
___bpf_prog_run() to a jump through __x86_indirect_thunk_rdx. objtool
puts that jump on the retpoline call list along with the indirect calls,
so with CONFIG_CFI=y the kCFI check wants a UD2 before it:

  vmlinux.o: warning: objtool: ___bpf_prog_run+0x1e: no-cfi indirect call!

The jump goes through the "jumptable" array, which objtool already reads
from .data.rel.ro.c_jump_table, so its targets stay inside the function
and need no kCFI check. Skip jump table jumps in the check. Clang does
not emit this jump: with retpolines, it lowers the computed goto without
an indirect jump.

Build tested ARCH=x86_64 defconfig with CONFIG_LKDTM=y and CONFIG_CFI=y,
with GCC 17.0.0 (experimental, with the kCFI series).

Assisted-by: LLM
Signed-off-by: Kees Cook <kees@kernel.org>
---
 tools/objtool/check.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 464f6c9d9ff0..d35c5305075f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4199,6 +4199,14 @@ static int validate_retpoline(struct objtool_file *file)
 	list_for_each_entry(insn, &file->retpoline_call_list, call_node) {
 		struct symbol *sym = insn_sym(insn);
 
+		/*
+		 * A jump through a jump table stays inside the function, so
+		 * it has no kCFI check.  GCC turns the computed goto in
+		 * ___bpf_prog_run() into one under MITIGATION_RETPOLINE.
+		 */
+		if (is_jump_table_jump(insn))
+			continue;
+
 		if (sym && (is_notype_sym(sym) ||
 			    is_func_sym(sym)) && !sym->nocfi) {
 			struct instruction *prev =
-- 
2.55.0


^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: [PATCH 2/3] x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte
  2026-10-12  9:04 ` [PATCH 2/3] x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte Kees Cook
@ 2026-10-12  9:16   ` Peter Zijlstra
  2026-10-12  9:59   ` [tip: x86/core] " tip-bot2 for Kees Cook
  1 sibling, 0 replies; 8+ messages in thread
From: Peter Zijlstra @ 2026-10-12  9:16 UTC (permalink / raw)
  To: Kees Cook
  Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen,
	H. Peter Anvin, Sami Tolvanen, Nathan Chancellor,
	Nick Desaulniers, Bill Wendling, Justin Stitt, x86, llvm,
	linux-kernel, linux-hardening

On Mon, Oct 12, 2026 at 02:04:25AM -0700, Kees Cook wrote:
> The "cs" prefix on the LEA in the FineIBT paranoid caller template is
> padding: it places the LEA's 0xf0 immediate byte where it doubles as the
> LOCK prefix that makes the failing Jcc raise #UD. GNU as warns about it
> in every CONFIG_FINEIBT=y build:
> 
>   Warning: segment override on `lea' is ineffectual

Shees...

^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: [PATCH 3/3] objtool: Skip jump table jumps in the kCFI indirect call check
  2026-10-12  9:04 ` [PATCH 3/3] objtool: Skip jump table jumps in the kCFI indirect call check Kees Cook
@ 2026-10-12  9:22   ` Peter Zijlstra
  0 siblings, 0 replies; 8+ messages in thread
From: Peter Zijlstra @ 2026-10-12  9:22 UTC (permalink / raw)
  To: Kees Cook
  Cc: Josh Poimboeuf, Sami Tolvanen, Nathan Chancellor,
	Nick Desaulniers, Bill Wendling, Justin Stitt, llvm,
	linux-kernel, linux-hardening

On Mon, Oct 12, 2026 at 02:04:26AM -0700, Kees Cook wrote:
> With MITIGATION_RETPOLINE=y, GCC lowers the computed goto in
> ___bpf_prog_run() to a jump through __x86_indirect_thunk_rdx. objtool
> puts that jump on the retpoline call list along with the indirect calls,
> so with CONFIG_CFI=y the kCFI check wants a UD2 before it:
> 
>   vmlinux.o: warning: objtool: ___bpf_prog_run+0x1e: no-cfi indirect call!
> 
> The jump goes through the "jumptable" array, which objtool already reads
> from .data.rel.ro.c_jump_table, so its targets stay inside the function
> and need no kCFI check. Skip jump table jumps in the check. Clang does
> not emit this jump: with retpolines, it lowers the computed goto without
> an indirect jump.

I am confused.. I don't see a computed goto in __bpf_prog_run(), and we
build with -fno-jump-tables.



^ permalink raw reply	[flat|nested] 8+ messages in thread

* [tip: x86/urgent] x86/kcfi: Decode the kCFI check from the trap address
  2026-10-12  9:04 ` [PATCH 1/3] x86/kcfi: Decode the kCFI check from the trap address Kees Cook
@ 2026-10-12  9:59   ` tip-bot2 for Kees Cook
  0 siblings, 0 replies; 8+ messages in thread
From: tip-bot2 for Kees Cook @ 2026-10-12  9:59 UTC (permalink / raw)
  To: linux-tip-commits; +Cc: Kees Cook, Peter Zijlstra (Intel), x86, linux-kernel

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

Commit-ID:     4505a262deae7df06e33617dfc104d5541eec91d
Gitweb:        https://git.kernel.org/tip/4505a262deae7df06e33617dfc104d5541eec91d
Author:        Kees Cook <kees@kernel.org>
AuthorDate:    Mon, 12 Oct 2026 02:04:24 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 12 Oct 2026 11:47:32 +02:00

x86/kcfi: Decode the kCFI check from the trap address

Since commit b2250d63e6422 ("x86/kcfi: Optimize call sequence"), a
CONFIG_FINEIBT=y kernel running in kCFI mode rewrites each kCFI call
site at boot so that a failed check traps on the 0xd6 byte of
"test $0xd6, %al", one byte past where the compiler's "ud2" was.
handle_cfi_failure() steps "addr" back one byte to find the trap in
.kcfi_traps, but decode_cfi_insn() still decodes from regs->ip, so it
reads each instruction starting at its second byte.
"movl $-<id>, %r10d" then decodes as "movl $-<id>, %edx", so the
reported type is right by accident, but "addl -15(%r11), %r10d" decodes
as "addl -15(%rbx), %edx", so the reported target is whatever %rbx holds:

  CFI failure at lkdtm_indirect_call+0x16/0x20 (target: 0x12; expected type: 0xc79a2d1b)

Pass the adjusted address to decode_cfi_insn() and decode from it.

Tested ARCH=x86_64 defconfig with CONFIG_CFI=y and CONFIG_LKDTM=y under
QEMU, with LKDTM's CFI_FORWARD_PROTO and both Clang 24.0.0git and GCC
17.0.0 (experimental, with the kCFI series). With CONFIG_FINEIBT=y in
kCFI mode, the report gives %rbx as the target without this change, and
the expected lkdtm_increment_int() with it. With cfi=fineibt, with
cfi=fineibt,paranoid, and with CONFIG_FINEIBT=n, it gives
lkdtm_increment_int() both with and without this change.

Fixes: b2250d63e6422 ("x86/kcfi: Optimize call sequence")
Assisted-by: LLM
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20261012090436.1676525-1-kees@kernel.org
---
 arch/x86/kernel/cfi.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cfi.c b/arch/x86/kernel/cfi.c
index 1df26df..8e5c4ed 100644
--- a/arch/x86/kernel/cfi.c
+++ b/arch/x86/kernel/cfi.c
@@ -10,11 +10,11 @@
 #include <asm/insn-eval.h>
 
 /*
- * Returns the target address and the expected type when regs->ip points
+ * Returns the target address and the expected type when addr points
  * to a compiler-generated CFI trap.
  */
-static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
-			    u32 *type)
+static bool decode_cfi_insn(struct pt_regs *regs, unsigned long addr,
+			    unsigned long *target, u32 *type)
 {
 	char buffer[MAX_INSN_SIZE];
 	struct insn insn;
@@ -29,13 +29,13 @@ static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
 	 *   movl    -<id>, %r10d       ; 6 bytes
 	 *   addl    -<pos>(%reg), %r10d; 4 bytes
 	 *   je      .Ltmp1             ; 2 bytes
-	 *   ud2                        ; <- regs->ip
+	 *   ud2                        ; <- addr
 	 *   .Ltmp1:
 	 *
 	 * We can decode the expected type and the target address from the
 	 * movl/addl instructions.
 	 */
-	if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 12, MAX_INSN_SIZE))
+	if (copy_from_kernel_nofault(buffer, (void *)addr - 12, MAX_INSN_SIZE))
 		return false;
 	if (insn_decode_kernel(&insn, &buffer[offset]))
 		return false;
@@ -44,7 +44,7 @@ static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
 
 	*type = -(u32)insn.immediate.value;
 
-	if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 6, MAX_INSN_SIZE))
+	if (copy_from_kernel_nofault(buffer, (void *)addr - 6, MAX_INSN_SIZE))
 		return false;
 	if (insn_decode_kernel(&insn, &buffer[offset]))
 		return false;
@@ -82,7 +82,7 @@ enum bug_trap_type handle_cfi_failure(struct pt_regs *regs)
 				return BUG_TRAP_TYPE_NONE;
 		}
 
-		if (!decode_cfi_insn(regs, &target, &type))
+		if (!decode_cfi_insn(regs, addr, &target, &type))
 			return report_cfi_failure_noaddr(regs, addr);
 
 		break;

^ permalink raw reply	[flat|nested] 8+ messages in thread

* [tip: x86/core] x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte
  2026-10-12  9:04 ` [PATCH 2/3] x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte Kees Cook
  2026-10-12  9:16   ` Peter Zijlstra
@ 2026-10-12  9:59   ` tip-bot2 for Kees Cook
  1 sibling, 0 replies; 8+ messages in thread
From: tip-bot2 for Kees Cook @ 2026-10-12  9:59 UTC (permalink / raw)
  To: linux-tip-commits; +Cc: Kees Cook, Peter Zijlstra (Intel), x86, linux-kernel

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

Commit-ID:     41d1119e2f8577b4bd01d31321c6761af9140ce7
Gitweb:        https://git.kernel.org/tip/41d1119e2f8577b4bd01d31321c6761af9140ce7
Author:        Kees Cook <kees@kernel.org>
AuthorDate:    Mon, 12 Oct 2026 02:04:25 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 12 Oct 2026 11:47:35 +02:00

x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte

The "cs" prefix on the LEA in the FineIBT paranoid caller template is
padding: it places the LEA's 0xf0 immediate byte where it doubles as the
LOCK prefix that makes the failing Jcc raise #UD. GNU as warns about it
in every CONFIG_FINEIBT=y build:

  Warning: segment override on `lea' is ineffectual

Clang's integrated assembler does not warn, and both assemble the same
bytes. Emit the prefix with ".byte 0x2e" to silence GNU as.

Build tested ARCH=x86_64 defconfig with CONFIG_CFI=y, with GCC 17.0.0
(experimental, with the kCFI series) and GNU as 2.47, and with Clang
24.0.0git: GNU as no longer warns, and the template assembles to the
same bytes as before with both. Under QEMU with cfi=fineibt,paranoid,
the paranoid caller check catches LKDTM's CFI_FORWARD_PROTO with both.

Assisted-by: LLM
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20261012090436.1676525-2-kees@kernel.org
---
 arch/x86/kernel/alternative.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 582c6d8..efbc11f 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1455,7 +1455,8 @@ asm(	".pushsection .rodata				\n"
 	"fineibt_paranoid_start:			\n"
 	"	mov	$0x12345678, %eax		\n"
 	"	cmpl	-11(%r11), %eax			\n"
-	"	cs lea	-0x10(%r11), %r11		\n"
+	"	.byte	0x2e				\n"
+	"	lea	-0x10(%r11), %r11		\n"
 	"#fineibt_caller_size:                          \n"
 	"	jne	fineibt_paranoid_start+0xd	\n"
 	"fineibt_paranoid_ind:				\n"

^ permalink raw reply	[flat|nested] 8+ messages in thread

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2026-10-12  9:04 [PATCH 0/3] x86/cfi: Fix a few kCFI issues found with GCC Kees Cook
2026-10-12  9:04 ` [PATCH 1/3] x86/kcfi: Decode the kCFI check from the trap address Kees Cook
2026-10-12  9:59   ` [tip: x86/urgent] " tip-bot2 for Kees Cook
2026-10-12  9:04 ` [PATCH 2/3] x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte Kees Cook
2026-10-12  9:16   ` Peter Zijlstra
2026-10-12  9:59   ` [tip: x86/core] " tip-bot2 for Kees Cook
2026-10-12  9:04 ` [PATCH 3/3] objtool: Skip jump table jumps in the kCFI indirect call check Kees Cook
2026-10-12  9:22   ` Peter Zijlstra

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