A recent change in LLVM causes module_{c,d}tor sections to appear when CONFIG_K{A,C}SAN are enabled, which results in orphan section warnings because these are not handled anywhere:
ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_ctor) is being placed in '.text.asan.module_ctor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_dtor) is being placed in '.text.asan.module_dtor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.tsan.module_ctor) is being placed in '.text.tsan.module_ctor'
Place them in the TEXT_TEXT section so that these technologies continue to work with the newer compiler versions. All of the KASAN and KCSAN KUnit tests continue to pass after this change.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1432 Link: https://github.com/llvm/llvm-project/commit/7b789562244ee941b7bf2cefeb3fc08a... Signed-off-by: Nathan Chancellor nathan@kernel.org --- include/asm-generic/vmlinux.lds.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 17325416e2de..3b79b1e76556 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -586,6 +586,7 @@ NOINSTR_TEXT \ *(.text..refcount) \ *(.ref.text) \ + *(.text.asan .text.asan.*) \ TEXT_CFI_JT \ MEM_KEEP(init.text*) \ MEM_KEEP(exit.text*) \
base-commit: 4669e13cd67f8532be12815ed3d37e775a9bdc16
On Fri, Jul 30, 2021 at 3:38 PM Nathan Chancellor nathan@kernel.org wrote:
A recent change in LLVM causes module_{c,d}tor sections to appear when CONFIG_K{A,C}SAN are enabled, which results in orphan section warnings because these are not handled anywhere:
ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_ctor) is being placed in '.text.asan.module_ctor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_dtor) is being placed in '.text.asan.module_dtor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.tsan.module_ctor) is being placed in '.text.tsan.module_ctor'
^ .text.tsan.*
Place them in the TEXT_TEXT section so that these technologies continue to work with the newer compiler versions. All of the KASAN and KCSAN KUnit tests continue to pass after this change.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1432 Link: https://github.com/llvm/llvm-project/commit/7b789562244ee941b7bf2cefeb3fc08a... Signed-off-by: Nathan Chancellor nathan@kernel.org
include/asm-generic/vmlinux.lds.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 17325416e2de..3b79b1e76556 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -586,6 +586,7 @@ NOINSTR_TEXT \ *(.text..refcount) \ *(.ref.text) \
*(.text.asan .text.asan.*) \
Will this match .text.tsan.module_ctor?
Do we want to add these conditionally on CONFIG_KASAN_GENERIC/CONFIG_KCSAN like we do for SANITIZER_DISCARDS?
TEXT_CFI_JT \ MEM_KEEP(init.text*) \ MEM_KEEP(exit.text*) \base-commit: 4669e13cd67f8532be12815ed3d37e775a9bdc16
On 2021-07-30, Nick Desaulniers wrote:
On Fri, Jul 30, 2021 at 3:38 PM Nathan Chancellor nathan@kernel.org wrote:
A recent change in LLVM causes module_{c,d}tor sections to appear when CONFIG_K{A,C}SAN are enabled, which results in orphan section warnings because these are not handled anywhere:
ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_ctor) is being placed in '.text.asan.module_ctor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_dtor) is being placed in '.text.asan.module_dtor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.tsan.module_ctor) is being placed in '.text.tsan.module_ctor'
^ .text.tsan.*
I was wondering why the orphan section warning only arose recently. Now I see: the function asan.module_ctor has the SHF_GNU_RETAIN flag, so it is in a separate section even with -fno-function-sections (default).
It seems that with -ffunction-sections the issue should have been caught much earlier.
Place them in the TEXT_TEXT section so that these technologies continue to work with the newer compiler versions. All of the KASAN and KCSAN KUnit tests continue to pass after this change.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1432 Link: https://github.com/llvm/llvm-project/commit/7b789562244ee941b7bf2cefeb3fc08a... Signed-off-by: Nathan Chancellor nathan@kernel.org
include/asm-generic/vmlinux.lds.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 17325416e2de..3b79b1e76556 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -586,6 +586,7 @@ NOINSTR_TEXT \ *(.text..refcount) \ *(.ref.text) \
*(.text.asan .text.asan.*) \Will this match .text.tsan.module_ctor?
asan.module_ctor is the only function AddressSanitizer synthesizes in the instrumented translation unit. There is no function called "asan".
(Even if a function "asan" exists due to -ffunction-sections -funique-section-names, TEXT_MAIN will match .text.asan, so the .text.asan pattern will match nothing.)
Do we want to add these conditionally on CONFIG_KASAN_GENERIC/CONFIG_KCSAN like we do for SANITIZER_DISCARDS?
TEXT_CFI_JT \ MEM_KEEP(init.text*) \ MEM_KEEP(exit.text*) \base-commit: 4669e13cd67f8532be12815ed3d37e775a9bdc16
-- Thanks, ~Nick Desaulniers
On 7/30/2021 3:59 PM, Fangrui Song wrote:
On 2021-07-30, Nick Desaulniers wrote:
On Fri, Jul 30, 2021 at 3:38 PM Nathan Chancellor nathan@kernel.org wrote:
A recent change in LLVM causes module_{c,d}tor sections to appear when CONFIG_K{A,C}SAN are enabled, which results in orphan section warnings because these are not handled anywhere:
ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_ctor) is being placed in '.text.asan.module_ctor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_dtor) is being placed in '.text.asan.module_dtor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.tsan.module_ctor) is being placed in '.text.tsan.module_ctor'
^ .text.tsan.*
I was wondering why the orphan section warning only arose recently. Now I see: the function asan.module_ctor has the SHF_GNU_RETAIN flag, so it is in a separate section even with -fno-function-sections (default).
Thanks for the explanation, I will add this to the commit message.
It seems that with -ffunction-sections the issue should have been caught much earlier.
Place them in the TEXT_TEXT section so that these technologies continue to work with the newer compiler versions. All of the KASAN and KCSAN KUnit tests continue to pass after this change.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1432 Link: https://github.com/llvm/llvm-project/commit/7b789562244ee941b7bf2cefeb3fc08a...
Signed-off-by: Nathan Chancellor nathan@kernel.org
include/asm-generic/vmlinux.lds.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 17325416e2de..3b79b1e76556 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -586,6 +586,7 @@ NOINSTR_TEXT \ *(.text..refcount) \ *(.ref.text) \ + *(.text.asan .text.asan.*) \
Will this match .text.tsan.module_ctor?
No, I forgot to test CONFIG_KCSAN with this version, rather than the prior one I had on GitHub so I will send v2 shortly.
asan.module_ctor is the only function AddressSanitizer synthesizes in the instrumented translation unit. There is no function called "asan".
(Even if a function "asan" exists due to -ffunction-sections -funique-section-names, TEXT_MAIN will match .text.asan, so the .text.asan pattern will match nothing.)
Sounds good, I will update it to remove the .text.asan and replace it with .text.tsan.*
Do we want to add these conditionally on CONFIG_KASAN_GENERIC/CONFIG_KCSAN like we do for SANITIZER_DISCARDS?
I do not think there is a point in doing so but I can if others feel strongly.
Thank you both for the comments for the comments!
Cheers, Nathan
A recent change in LLVM causes module_{c,d}tor sections to appear when CONFIG_K{A,C}SAN are enabled, which results in orphan section warnings because these are not handled anywhere:
ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_ctor) is being placed in '.text.asan.module_ctor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_dtor) is being placed in '.text.asan.module_dtor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.tsan.module_ctor) is being placed in '.text.tsan.module_ctor'
Fangrui explains: "the function asan.module_ctor has the SHF_GNU_RETAIN flag, so it is in a separate section even with -fno-function-sections (default)".
Place them in the TEXT_TEXT section so that these technologies continue to work with the newer compiler versions. All of the KASAN and KCSAN KUnit tests continue to pass after this change.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1432 Link: https://github.com/llvm/llvm-project/commit/7b789562244ee941b7bf2cefeb3fc08a... Signed-off-by: Nathan Chancellor nathan@kernel.org ---
v1 -> v2:
* Fix inclusion of .text.tsan.* (Nick)
* Drop .text.asan as it does not exist plus it would be handled by a different line (Fangrui)
* Add Fangrui's explanation about why the LLVM commit caused these sections to appear.
include/asm-generic/vmlinux.lds.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 17325416e2de..62669b36a772 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -586,6 +586,7 @@ NOINSTR_TEXT \ *(.text..refcount) \ *(.ref.text) \ + *(.text.asan.* .text.tsan.*) \ TEXT_CFI_JT \ MEM_KEEP(init.text*) \ MEM_KEEP(exit.text*) \
base-commit: 4669e13cd67f8532be12815ed3d37e775a9bdc16
Reviewed-by: Fangrui Song maskray@google.com
On 2021-07-30, Nathan Chancellor wrote:
A recent change in LLVM causes module_{c,d}tor sections to appear when CONFIG_K{A,C}SAN are enabled, which results in orphan section warnings because these are not handled anywhere:
ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_ctor) is being placed in '.text.asan.module_ctor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_dtor) is being placed in '.text.asan.module_dtor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.tsan.module_ctor) is being placed in '.text.tsan.module_ctor'
Fangrui explains: "the function asan.module_ctor has the SHF_GNU_RETAIN flag, so it is in a separate section even with -fno-function-sections (default)".
If my theory is true, we should see orphan section warning with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION before my sanitizer change.
Place them in the TEXT_TEXT section so that these technologies continue to work with the newer compiler versions. All of the KASAN and KCSAN KUnit tests continue to pass after this change.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1432 Link: https://github.com/llvm/llvm-project/commit/7b789562244ee941b7bf2cefeb3fc08a... Signed-off-by: Nathan Chancellor nathan@kernel.org
v1 -> v2:
Fix inclusion of .text.tsan.* (Nick)
Drop .text.asan as it does not exist plus it would be handled by a
different line (Fangrui)
- Add Fangrui's explanation about why the LLVM commit caused these
sections to appear.
include/asm-generic/vmlinux.lds.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 17325416e2de..62669b36a772 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -586,6 +586,7 @@ NOINSTR_TEXT \ *(.text..refcount) \ *(.ref.text) \
*(.text.asan.* .text.tsan.*) \
When kmsan is upstreamed, we may need to add .text.msan.* :)
( I wondered why we cannot just change the TEXT_MAIN pattern to .text.*
For large userspace applications, separating .text.unlikely .text.hot can help do things like hugepage and mlock, which can improve instruction cache localize and reduce instruction TLB miss rates,,, but not sure this helps much for the kernel.
Or perhaps some .text.FOOBAR has special usage which cannot be placed into the output .text )
TEXT_CFI_JT \MEM_KEEP(init.text*) \ MEM_KEEP(exit.text*) \
base-commit: 4669e13cd67f8532be12815ed3d37e775a9bdc16
2.32.0.264.g75ae10bc75
On Sat, 31 Jul 2021 at 04:33, Nathan Chancellor nathan@kernel.org wrote:
A recent change in LLVM causes module_{c,d}tor sections to appear when CONFIG_K{A,C}SAN are enabled, which results in orphan section warnings because these are not handled anywhere:
ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_ctor) is being placed in '.text.asan.module_ctor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_dtor) is being placed in '.text.asan.module_dtor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.tsan.module_ctor) is being placed in '.text.tsan.module_ctor'
Fangrui explains: "the function asan.module_ctor has the SHF_GNU_RETAIN flag, so it is in a separate section even with -fno-function-sections (default)".
Place them in the TEXT_TEXT section so that these technologies continue to work with the newer compiler versions. All of the KASAN and KCSAN KUnit tests continue to pass after this change.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1432 Link: https://github.com/llvm/llvm-project/commit/7b789562244ee941b7bf2cefeb3fc08a... Signed-off-by: Nathan Chancellor nathan@kernel.org
Acked-by: Marco Elver elver@google.com
For KASAN module_ctors are very much required to support detecting globals out-of-bounds: https://reviews.llvm.org/D81390 For KASAN the test would have revealed that at the latest.
KCSAN does not yet have much use for the module_ctors, but it may change in future, so keeping them all was the right call.
Thanks, -- Marco
v1 -> v2:
Fix inclusion of .text.tsan.* (Nick)
Drop .text.asan as it does not exist plus it would be handled by a different line (Fangrui)
Add Fangrui's explanation about why the LLVM commit caused these sections to appear.
include/asm-generic/vmlinux.lds.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 17325416e2de..62669b36a772 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -586,6 +586,7 @@ NOINSTR_TEXT \ *(.text..refcount) \ *(.ref.text) \
*(.text.asan.* .text.tsan.*) \ TEXT_CFI_JT \ MEM_KEEP(init.text*) \ MEM_KEEP(exit.text*) \base-commit: 4669e13cd67f8532be12815ed3d37e775a9bdc16
2.32.0.264.g75ae10bc75
On Fri, Jul 30, 2021 at 7:33 PM Nathan Chancellor nathan@kernel.org wrote:
A recent change in LLVM causes module_{c,d}tor sections to appear when CONFIG_K{A,C}SAN are enabled, which results in orphan section warnings because these are not handled anywhere:
ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_ctor) is being placed in '.text.asan.module_ctor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_dtor) is being placed in '.text.asan.module_dtor' ld.lld: warning: arch/x86/pci/built-in.a(legacy.o):(.text.tsan.module_ctor) is being placed in '.text.tsan.module_ctor'
Fangrui explains: "the function asan.module_ctor has the SHF_GNU_RETAIN flag, so it is in a separate section even with -fno-function-sections (default)".
Place them in the TEXT_TEXT section so that these technologies continue to work with the newer compiler versions. All of the KASAN and KCSAN KUnit tests continue to pass after this change.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1432 Link: https://github.com/llvm/llvm-project/commit/7b789562244ee941b7bf2cefeb3fc08a... Signed-off-by: Nathan Chancellor nathan@kernel.org
Reviewed-by: Nick Desaulniers ndesaulniers@google.com
v1 -> v2:
Fix inclusion of .text.tsan.* (Nick)
Drop .text.asan as it does not exist plus it would be handled by a different line (Fangrui)
Add Fangrui's explanation about why the LLVM commit caused these sections to appear.
include/asm-generic/vmlinux.lds.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 17325416e2de..62669b36a772 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -586,6 +586,7 @@ NOINSTR_TEXT \ *(.text..refcount) \ *(.ref.text) \
*(.text.asan.* .text.tsan.*) \ TEXT_CFI_JT \ MEM_KEEP(init.text*) \ MEM_KEEP(exit.text*) \base-commit: 4669e13cd67f8532be12815ed3d37e775a9bdc16
2.32.0.264.g75ae10bc75
linux-stable-mirror@lists.linaro.org
-
Fangrui Song -
Marco Elver -
Nathan Chancellor -
Nick Desaulniers