[PATCH tip] x86/percpu: Disable named address spaces for KASAN

[PATCH tip] x86/percpu: Disable named address spaces for KASAN

[Uros Bizjak]

-fsanitize=kernel-address (KASAN) is at the moment incompatible
with named address spaces - see GCC PR sanitizer/111736.

GCC is doing a KASAN check on a percpu address which it shouldn't do,
and didn't used to do because we did the access using inline asm.

But now that GCC does the accesses as normal (albeit special address
space) memory accesses, the KASAN code triggers on them too, and it
all goes to hell in a handbasket very quickly.

Those percpu accessor functions need to disable any KASAN
checking or other sanitizer checking. Not on the percpu address,
because that's not a "real" address, it's obviously just the offset
from the segment register.

And GCC should probably not have generated such code in the first
place, so arguably this is a bug with -fsanitize=kernel-address.

The patch also removes a stale dependency on CONFIG_SMP.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202310071301.a5113890-oliver.sang@intel.com
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Nadav Amit <namit@vmware.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
 arch/x86/Kconfig | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ecb256954351..54e79d3061f9 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2393,7 +2393,12 @@ config CC_HAS_NAMED_AS
 
 config USE_X86_SEG_SUPPORT
 	def_bool y
-	depends on CC_HAS_NAMED_AS && SMP
+	depends on CC_HAS_NAMED_AS
+	#
+	# -fsanitize=kernel-address (KASAN) is at the moment incompatible
+	# with named address spaces - see GCC PR sanitizer/111736.
+	#
+	depends on !KASAN
 
 config CC_HAS_SLS
 	def_bool $(cc-option,-mharden-sls=all)
-- 
2.41.0

[tip: x86/percpu] x86/percpu: Disable named address spaces for KASAN

[tip-bot2 for Uros Bizjak]

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

Commit-ID:     a3c7a64f9b764e200338130253dfe4488db03f4f
Gitweb:        https://git.kernel.org/tip/a3c7a64f9b764e200338130253dfe4488db03f4f
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Mon, 09 Oct 2023 17:13:48 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 09 Oct 2023 17:45:05 +02:00

x86/percpu: Disable named address spaces for KASAN

-fsanitize=kernel-address (KASAN) is at the moment incompatible
with named address spaces - see GCC PR sanitizer/111736:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111736

GCC is doing a KASAN check on a percpu address which it shouldn't do,
and didn't used to do because we did the access using inline asm.

But now that GCC does the accesses as normal (albeit special address
space) memory accesses, the KASAN code triggers on them too, and it
all goes to hell in a handbasket very quickly.

Those percpu accessor functions need to disable any KASAN
checking or other sanitizer checking. Not on the percpu address,
because that's not a "real" address, it's obviously just the offset
from the segment register.

And GCC should probably not have generated such code in the first
place, so arguably this is a bug with -fsanitize=kernel-address.

The patch also removes a stale dependency on CONFIG_SMP.

Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231009151409.53656-1-ubizjak@gmail.com

Closes: https://lore.kernel.org/oe-lkp/202310071301.a5113890-oliver.sang@intel.com
---
 arch/x86/Kconfig | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ecb2569..54e79d3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2393,7 +2393,12 @@ config CC_HAS_NAMED_AS
 
 config USE_X86_SEG_SUPPORT
 	def_bool y
-	depends on CC_HAS_NAMED_AS && SMP
+	depends on CC_HAS_NAMED_AS
+	#
+	# -fsanitize=kernel-address (KASAN) is at the moment incompatible
+	# with named address spaces - see GCC PR sanitizer/111736.
+	#
+	depends on !KASAN
 
 config CC_HAS_SLS
 	def_bool $(cc-option,-mharden-sls=all)

[tip: x86/percpu] x86/percpu: Disable named address spaces for KASAN

[tip-bot2 for Uros Bizjak]

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

Commit-ID:     e29aad08b1da7772b362537be32335c0394e65fe
Gitweb:        https://git.kernel.org/tip/e29aad08b1da7772b362537be32335c0394e65fe
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Mon, 09 Oct 2023 17:13:48 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 10 Oct 2023 23:57:35 +02:00

x86/percpu: Disable named address spaces for KASAN

-fsanitize=kernel-address (KASAN) is at the moment incompatible
with named address spaces - see GCC PR sanitizer/111736:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111736

GCC is doing a KASAN check on a percpu address which it shouldn't do,
and didn't used to do because we did the access using inline asm.

But now that GCC does the accesses as normal (albeit special address
space) memory accesses, the KASAN code triggers on them too, and it
all goes to hell in a handbasket very quickly.

Those percpu accessor functions need to disable any KASAN
checking or other sanitizer checking. Not on the percpu address,
because that's not a "real" address, it's obviously just the offset
from the segment register.

And GCC should probably not have generated such code in the first
place, so arguably this is a bug with -fsanitize=kernel-address.

The patch also removes a stale dependency on CONFIG_SMP.

Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20231009151409.53656-1-ubizjak@gmail.com

Closes: https://lore.kernel.org/oe-lkp/202310071301.a5113890-oliver.sang@intel.com
---
 arch/x86/Kconfig | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ecb2569..54e79d3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2393,7 +2393,12 @@ config CC_HAS_NAMED_AS
 
 config USE_X86_SEG_SUPPORT
 	def_bool y
-	depends on CC_HAS_NAMED_AS && SMP
+	depends on CC_HAS_NAMED_AS
+	#
+	# -fsanitize=kernel-address (KASAN) is at the moment incompatible
+	# with named address spaces - see GCC PR sanitizer/111736.
+	#
+	depends on !KASAN
 
 config CC_HAS_SLS
 	def_bool $(cc-option,-mharden-sls=all)