* [PATCH 0/3] cfi: Use __builtin_function_start @ 2022-04-01 20:19 Sami Tolvanen 2022-04-01 20:19 ` [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start Sami Tolvanen ` (3 more replies) 0 siblings, 4 replies; 12+ messages in thread From: Sami Tolvanen @ 2022-04-01 20:19 UTC (permalink / raw) To: Kees Cook Cc: Catalin Marinas, Mark Rutland, Masahiro Yamada, Nathan Chancellor, Nick Desaulniers, Will Deacon, linux-arm-kernel, linux-kernel, llvm, Sami Tolvanen Clang 14 introduced the __builtin_function_start intrinsic, which makes it possible to cleanly implement the function_nocfi() macro in a way that also works with static initializers. Add a default function_nocfi() implementation and drop the arm64 inline assembly version. Sami Tolvanen (3): kbuild: Change CFI_CLANG to depend on __builtin_function_start linux/compiler-clang.h: define function_nocfi arm64: Drop the inline assembly implementation of function_nocfi arch/Kconfig | 5 +---- arch/arm64/include/asm/compiler.h | 16 ---------------- include/linux/compiler-clang.h | 10 ++++++++++ init/Kconfig | 3 +++ 4 files changed, 14 insertions(+), 20 deletions(-) -- 2.35.0 ^ permalink raw reply [flat|nested] 12+ messages in thread
* [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start 2022-04-01 20:19 [PATCH 0/3] cfi: Use __builtin_function_start Sami Tolvanen @ 2022-04-01 20:19 ` Sami Tolvanen 2022-04-02 13:31 ` Masahiro Yamada 2022-04-01 20:19 ` [PATCH 2/3] linux/compiler-clang.h: define function_nocfi Sami Tolvanen ` (2 subsequent siblings) 3 siblings, 1 reply; 12+ messages in thread From: Sami Tolvanen @ 2022-04-01 20:19 UTC (permalink / raw) To: Kees Cook Cc: Catalin Marinas, Mark Rutland, Masahiro Yamada, Nathan Chancellor, Nick Desaulniers, Will Deacon, linux-arm-kernel, linux-kernel, llvm, Sami Tolvanen Clang 14 added support for the __builtin_function_start() built-in function, which allows us to implement function_nocfi() without architecture-specific inline assembly. This patch changes CONFIG_CFI_CLANG to depend on the built-in and effectively upgrades the minimum supported compiler version for CFI to Clang 14. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- arch/Kconfig | 5 +---- init/Kconfig | 3 +++ 2 files changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/Kconfig b/arch/Kconfig index 29b0167c088b..eecfc2809781 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -723,10 +723,7 @@ config ARCH_SUPPORTS_CFI_CLANG config CFI_CLANG bool "Use Clang's Control Flow Integrity (CFI)" depends on LTO_CLANG && ARCH_SUPPORTS_CFI_CLANG - # Clang >= 12: - # - https://bugs.llvm.org/show_bug.cgi?id=46258 - # - https://bugs.llvm.org/show_bug.cgi?id=47479 - depends on CLANG_VERSION >= 120000 + depends on CC_HAS_BUILTIN_FUNCTION_START select KALLSYMS help This option enables Clang’s forward-edge Control Flow Integrity diff --git a/init/Kconfig b/init/Kconfig index ddcbefe535e9..f024fd353373 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -86,6 +86,9 @@ config CC_HAS_ASM_INLINE config CC_HAS_NO_PROFILE_FN_ATTR def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror) +config CC_HAS_BUILTIN_FUNCTION_START + def_bool $(success,echo 'void f(void) {}; void *p = __builtin_function_start(f);' | $(CC) -x c - -c -o /dev/null) + config PAHOLE_VERSION int default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE)) -- 2.35.0 ^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start 2022-04-01 20:19 ` [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start Sami Tolvanen @ 2022-04-02 13:31 ` Masahiro Yamada 2022-04-04 19:40 ` Sami Tolvanen 0 siblings, 1 reply; 12+ messages in thread From: Masahiro Yamada @ 2022-04-02 13:31 UTC (permalink / raw) To: Sami Tolvanen Cc: Kees Cook, Catalin Marinas, Mark Rutland, Nathan Chancellor, Nick Desaulniers, Will Deacon, linux-arm-kernel, Linux Kernel Mailing List, llvm On Sat, Apr 2, 2022 at 5:19 AM Sami Tolvanen <samitolvanen@google.com> wrote: > > Clang 14 added support for the __builtin_function_start() > built-in function, which allows us to implement function_nocfi() > without architecture-specific inline assembly. This patch changes > CONFIG_CFI_CLANG to depend on the built-in and effectively upgrades > the minimum supported compiler version for CFI to Clang 14. From this description, I think the straight-forward change would be: depends on CLANG_VERSION >= 120000 --> depends on CLANG_VERSION >= 140000 Any reason to avoid this? > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > arch/Kconfig | 5 +---- > init/Kconfig | 3 +++ > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/arch/Kconfig b/arch/Kconfig > index 29b0167c088b..eecfc2809781 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -723,10 +723,7 @@ config ARCH_SUPPORTS_CFI_CLANG > config CFI_CLANG > bool "Use Clang's Control Flow Integrity (CFI)" > depends on LTO_CLANG && ARCH_SUPPORTS_CFI_CLANG > - # Clang >= 12: > - # - https://bugs.llvm.org/show_bug.cgi?id=46258 > - # - https://bugs.llvm.org/show_bug.cgi?id=47479 > - depends on CLANG_VERSION >= 120000 > + depends on CC_HAS_BUILTIN_FUNCTION_START > select KALLSYMS > help > This option enables Clang’s forward-edge Control Flow Integrity > diff --git a/init/Kconfig b/init/Kconfig > index ddcbefe535e9..f024fd353373 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -86,6 +86,9 @@ config CC_HAS_ASM_INLINE > config CC_HAS_NO_PROFILE_FN_ATTR > def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror) > > +config CC_HAS_BUILTIN_FUNCTION_START > + def_bool $(success,echo 'void f(void) {}; void *p = __builtin_function_start(f);' | $(CC) -x c - -c -o /dev/null) > + > config PAHOLE_VERSION > int > default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE)) > -- > 2.35.0 > -- Best Regards Masahiro Yamada ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start 2022-04-02 13:31 ` Masahiro Yamada @ 2022-04-04 19:40 ` Sami Tolvanen 2022-04-04 22:52 ` Nathan Chancellor 0 siblings, 1 reply; 12+ messages in thread From: Sami Tolvanen @ 2022-04-04 19:40 UTC (permalink / raw) To: Masahiro Yamada Cc: Kees Cook, Catalin Marinas, Mark Rutland, Nathan Chancellor, Nick Desaulniers, Will Deacon, linux-arm-kernel, Linux Kernel Mailing List, llvm On Sat, Apr 2, 2022 at 6:32 AM Masahiro Yamada <masahiroy@kernel.org> wrote: > > On Sat, Apr 2, 2022 at 5:19 AM Sami Tolvanen <samitolvanen@google.com> wrote: > > > > Clang 14 added support for the __builtin_function_start() > > built-in function, which allows us to implement function_nocfi() > > without architecture-specific inline assembly. This patch changes > > CONFIG_CFI_CLANG to depend on the built-in and effectively upgrades > > the minimum supported compiler version for CFI to Clang 14. > > From this description, I think the straight-forward change would be: > > depends on CLANG_VERSION >= 120000 > --> > depends on CLANG_VERSION >= 140000 > > Any reason to avoid this? I thought testing for the compiler feature was preferred, but I can certainly just increase the minimum version number here too. Sami ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start 2022-04-04 19:40 ` Sami Tolvanen @ 2022-04-04 22:52 ` Nathan Chancellor 2022-04-05 2:53 ` Kees Cook 0 siblings, 1 reply; 12+ messages in thread From: Nathan Chancellor @ 2022-04-04 22:52 UTC (permalink / raw) To: Sami Tolvanen Cc: Masahiro Yamada, Kees Cook, Catalin Marinas, Mark Rutland, Nick Desaulniers, Will Deacon, linux-arm-kernel, Linux Kernel Mailing List, llvm On Mon, Apr 04, 2022 at 12:40:46PM -0700, Sami Tolvanen wrote: > On Sat, Apr 2, 2022 at 6:32 AM Masahiro Yamada <masahiroy@kernel.org> wrote: > > > > On Sat, Apr 2, 2022 at 5:19 AM Sami Tolvanen <samitolvanen@google.com> wrote: > > > > > > Clang 14 added support for the __builtin_function_start() > > > built-in function, which allows us to implement function_nocfi() > > > without architecture-specific inline assembly. This patch changes > > > CONFIG_CFI_CLANG to depend on the built-in and effectively upgrades > > > the minimum supported compiler version for CFI to Clang 14. > > > > From this description, I think the straight-forward change would be: > > > > depends on CLANG_VERSION >= 120000 > > --> > > depends on CLANG_VERSION >= 140000 > > > > Any reason to avoid this? > > I thought testing for the compiler feature was preferred, but I can > certainly just increase the minimum version number here too. I think we have been somewhat inconsistent with feature versus version checking. It might be nice to hash out when a feature check should be done instead of a version one. Generally, I think we tend to prefer version checks, as they are "cheaper" since we do not have to call the compiler again because we already cached the version code. When adding version checks, our policy has always been use the upstream version of LLVM that the feature in question shipped in, even if it is a top of tree version, as people who are using prereleased versions of LLVM should be frequently updating them. Unfortunately, that does not always match reality. For example, Android's LLVM tracks the main branch but they are almost always behind by a few months. For example, the latest release is 14.0.4, based on a version of LLVM from January 28th: https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/+/ab73cd180863dbd17fdb8f20e39b33ab38030cf9/clang-r450784b/clang_source_info.md https://github.com/llvm/llvm-project/commits/282c83c32384cb2f37030c28650fef4150a8b67c Normally, I would say "who cares?" but Android's LLVM is used by the Android kernel team both downstream and upstream, so I would argue it is important to take that into account when deciding to do a feature check versus a version check. In other words, by moving to a version check, will we knowingly break a version of clang that is relatively widely used? In this case, 14.0.4 has __builtin_function_start(), so I think it is okay to use a version check instead of a feature one. There are times where feature or problem checking is not always possible: https://lore.kernel.org/r/20220318230747.3900772-1-nathan@kernel.org/ In cases like these, we can work to upgrade the compiler before changing the feature check ot a version one, which helps minimize the window for breakage. Another aspect of feature versus version checks is that it is easier to clean up stale versions checks when we bump the minimum supported version of the compiler (as we can just look for "CLANG_VERSION" across the tree) compared to stale feature checks. We could fix this by adding some sort of common keyword, like Compiler check: <compiler> <comparison> <version> like Compiler check: clang <= 14.0.0 Cheers, Nathan ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start 2022-04-04 22:52 ` Nathan Chancellor @ 2022-04-05 2:53 ` Kees Cook 0 siblings, 0 replies; 12+ messages in thread From: Kees Cook @ 2022-04-05 2:53 UTC (permalink / raw) To: Nathan Chancellor Cc: Sami Tolvanen, Masahiro Yamada, Catalin Marinas, Mark Rutland, Nick Desaulniers, Will Deacon, linux-arm-kernel, Linux Kernel Mailing List, llvm On Mon, Apr 04, 2022 at 03:52:11PM -0700, Nathan Chancellor wrote: > On Mon, Apr 04, 2022 at 12:40:46PM -0700, Sami Tolvanen wrote: > > On Sat, Apr 2, 2022 at 6:32 AM Masahiro Yamada <masahiroy@kernel.org> wrote: > > > > > > On Sat, Apr 2, 2022 at 5:19 AM Sami Tolvanen <samitolvanen@google.com> wrote: > > > > > > > > Clang 14 added support for the __builtin_function_start() > > > > built-in function, which allows us to implement function_nocfi() > > > > without architecture-specific inline assembly. This patch changes > > > > CONFIG_CFI_CLANG to depend on the built-in and effectively upgrades > > > > the minimum supported compiler version for CFI to Clang 14. > > > > > > From this description, I think the straight-forward change would be: > > > > > > depends on CLANG_VERSION >= 120000 > > > --> > > > depends on CLANG_VERSION >= 140000 > > > > > > Any reason to avoid this? > > > > I thought testing for the compiler feature was preferred, but I can > > certainly just increase the minimum version number here too. > > I think we have been somewhat inconsistent with feature versus version > checking. It might be nice to hash out when a feature check should be > done instead of a version one. > > Generally, I think we tend to prefer version checks, as they are > "cheaper" since we do not have to call the compiler again because we > already cached the version code. When adding version checks, our policy > has always been use the upstream version of LLVM that the feature in > question shipped in, even if it is a top of tree version, as people who > are using prereleased versions of LLVM should be frequently updating > them. > > Unfortunately, that does not always match reality. For example, > Android's LLVM tracks the main branch but they are almost always behind > by a few months. For example, the latest release is 14.0.4, based on a > version of LLVM from January 28th: > > https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/+/ab73cd180863dbd17fdb8f20e39b33ab38030cf9/clang-r450784b/clang_source_info.md > https://github.com/llvm/llvm-project/commits/282c83c32384cb2f37030c28650fef4150a8b67c > > Normally, I would say "who cares?" but Android's LLVM is used by the > Android kernel team both downstream and upstream, so I would argue it is > important to take that into account when deciding to do a feature check > versus a version check. In other words, by moving to a version check, > will we knowingly break a version of clang that is relatively widely > used? > > In this case, 14.0.4 has __builtin_function_start(), so I think it is > okay to use a version check instead of a feature one. Thanks for checking the details on that. Yeah, I think it's fine to go with a version check here. Sami, can you send a v2, and I can take it via the hardening for -next? (Unless the ARM folks _really_ want it for -rc2 -- this is kind of a fix, but it's also kind of not.) -- Kees Cook ^ permalink raw reply [flat|nested] 12+ messages in thread
* [PATCH 2/3] linux/compiler-clang.h: define function_nocfi 2022-04-01 20:19 [PATCH 0/3] cfi: Use __builtin_function_start Sami Tolvanen 2022-04-01 20:19 ` [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start Sami Tolvanen @ 2022-04-01 20:19 ` Sami Tolvanen 2022-04-05 16:16 ` Mark Rutland 2022-04-01 20:19 ` [PATCH 3/3] arm64: Drop the inline assembly implementation of function_nocfi Sami Tolvanen 2022-04-01 20:49 ` [PATCH 0/3] cfi: Use __builtin_function_start Nick Desaulniers 3 siblings, 1 reply; 12+ messages in thread From: Sami Tolvanen @ 2022-04-01 20:19 UTC (permalink / raw) To: Kees Cook Cc: Catalin Marinas, Mark Rutland, Masahiro Yamada, Nathan Chancellor, Nick Desaulniers, Will Deacon, linux-arm-kernel, linux-kernel, llvm, Sami Tolvanen Use __builtin_function_start() to implement the function_nocfi() macro when CONFIG_CFI_CLANG is selected. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- include/linux/compiler-clang.h | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index babb1347148c..c84fec767445 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -69,6 +69,16 @@ #define __nocfi __attribute__((__no_sanitize__("cfi"))) #define __cficanonical __attribute__((__cfi_canonical_jump_table__)) +#if defined(CONFIG_CFI_CLANG) +/* + * With CONFIG_CFI_CLANG, the compiler replaces function address + * references with the address of the function's CFI jump table + * entry. The function_nocfi macro always returns the address of the + * actual function instead. + */ +#define function_nocfi(x) __builtin_function_start(x) +#endif + /* * Turn individual warnings and errors on and off locally, depending * on version. -- 2.35.0 ^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH 2/3] linux/compiler-clang.h: define function_nocfi 2022-04-01 20:19 ` [PATCH 2/3] linux/compiler-clang.h: define function_nocfi Sami Tolvanen @ 2022-04-05 16:16 ` Mark Rutland 0 siblings, 0 replies; 12+ messages in thread From: Mark Rutland @ 2022-04-05 16:16 UTC (permalink / raw) To: Sami Tolvanen Cc: Kees Cook, Catalin Marinas, Masahiro Yamada, Nathan Chancellor, Nick Desaulniers, Will Deacon, linux-arm-kernel, linux-kernel, llvm On Fri, Apr 01, 2022 at 01:19:15PM -0700, Sami Tolvanen wrote: > Use __builtin_function_start() to implement the function_nocfi() macro > when CONFIG_CFI_CLANG is selected. > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > include/linux/compiler-clang.h | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h > index babb1347148c..c84fec767445 100644 > --- a/include/linux/compiler-clang.h > +++ b/include/linux/compiler-clang.h > @@ -69,6 +69,16 @@ > #define __nocfi __attribute__((__no_sanitize__("cfi"))) > #define __cficanonical __attribute__((__cfi_canonical_jump_table__)) > > +#if defined(CONFIG_CFI_CLANG) > +/* > + * With CONFIG_CFI_CLANG, the compiler replaces function address > + * references with the address of the function's CFI jump table > + * entry. The function_nocfi macro always returns the address of the > + * actual function instead. > + */ > +#define function_nocfi(x) __builtin_function_start(x) > +#endif As a heads-up, with patches 1 and 2 applied (but not patch 3), we have two definitions of function_nocfi(), which casues the compiler to scream for every object: | In file included from <built-in>:3: | In file included from ././include/linux/compiler_types.h:107: | ./arch/arm64/include/asm/compiler.h:33:9: warning: 'function_nocfi' macro redefined [-Wmacro-redefined] | #define function_nocfi(x) ({ \ | ^ | ./include/linux/compiler-clang.h:79:9: note: previous definition is here | #define function_nocfi(x) __builtin_function_start(x) | ^ | 1 warning generated. ... which would be painful for bisection. I suspect It's probably worth folding patches 2 and 3 together to avoid that? Arguably we could fold the entire series together into one commit at that point. Thanks, Mark. ^ permalink raw reply [flat|nested] 12+ messages in thread
* [PATCH 3/3] arm64: Drop the inline assembly implementation of function_nocfi 2022-04-01 20:19 [PATCH 0/3] cfi: Use __builtin_function_start Sami Tolvanen 2022-04-01 20:19 ` [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start Sami Tolvanen 2022-04-01 20:19 ` [PATCH 2/3] linux/compiler-clang.h: define function_nocfi Sami Tolvanen @ 2022-04-01 20:19 ` Sami Tolvanen 2022-04-04 9:03 ` Will Deacon 2022-04-05 16:23 ` Mark Rutland 2022-04-01 20:49 ` [PATCH 0/3] cfi: Use __builtin_function_start Nick Desaulniers 3 siblings, 2 replies; 12+ messages in thread From: Sami Tolvanen @ 2022-04-01 20:19 UTC (permalink / raw) To: Kees Cook Cc: Catalin Marinas, Mark Rutland, Masahiro Yamada, Nathan Chancellor, Nick Desaulniers, Will Deacon, linux-arm-kernel, linux-kernel, llvm, Sami Tolvanen Drop the inline assembly version of function_nocfi() now that CONFIG_CFI_CLANG depends on __builtin_function_start(), which allows this macro to be implemented more cleanly and in a way that works also with static initializers. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- arch/arm64/include/asm/compiler.h | 16 ---------------- 1 file changed, 16 deletions(-) diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h index dc3ea4080e2e..6fb2e6bcc392 100644 --- a/arch/arm64/include/asm/compiler.h +++ b/arch/arm64/include/asm/compiler.h @@ -23,20 +23,4 @@ #define __builtin_return_address(val) \ (void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val))) -#ifdef CONFIG_CFI_CLANG -/* - * With CONFIG_CFI_CLANG, the compiler replaces function address - * references with the address of the function's CFI jump table - * entry. The function_nocfi macro always returns the address of the - * actual function instead. - */ -#define function_nocfi(x) ({ \ - void *addr; \ - asm("adrp %0, " __stringify(x) "\n\t" \ - "add %0, %0, :lo12:" __stringify(x) \ - : "=r" (addr)); \ - addr; \ -}) -#endif - #endif /* __ASM_COMPILER_H */ -- 2.35.0 ^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH 3/3] arm64: Drop the inline assembly implementation of function_nocfi 2022-04-01 20:19 ` [PATCH 3/3] arm64: Drop the inline assembly implementation of function_nocfi Sami Tolvanen @ 2022-04-04 9:03 ` Will Deacon 2022-04-05 16:23 ` Mark Rutland 1 sibling, 0 replies; 12+ messages in thread From: Will Deacon @ 2022-04-04 9:03 UTC (permalink / raw) To: Sami Tolvanen Cc: Kees Cook, Catalin Marinas, Mark Rutland, Masahiro Yamada, Nathan Chancellor, Nick Desaulniers, linux-arm-kernel, linux-kernel, llvm On Fri, Apr 01, 2022 at 01:19:16PM -0700, Sami Tolvanen wrote: > Drop the inline assembly version of function_nocfi() now that > CONFIG_CFI_CLANG depends on __builtin_function_start(), which allows > this macro to be implemented more cleanly and in a way that works also > with static initializers. > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > arch/arm64/include/asm/compiler.h | 16 ---------------- > 1 file changed, 16 deletions(-) > > diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h > index dc3ea4080e2e..6fb2e6bcc392 100644 > --- a/arch/arm64/include/asm/compiler.h > +++ b/arch/arm64/include/asm/compiler.h > @@ -23,20 +23,4 @@ > #define __builtin_return_address(val) \ > (void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val))) > > -#ifdef CONFIG_CFI_CLANG > -/* > - * With CONFIG_CFI_CLANG, the compiler replaces function address > - * references with the address of the function's CFI jump table > - * entry. The function_nocfi macro always returns the address of the > - * actual function instead. > - */ > -#define function_nocfi(x) ({ \ > - void *addr; \ > - asm("adrp %0, " __stringify(x) "\n\t" \ > - "add %0, %0, :lo12:" __stringify(x) \ > - : "=r" (addr)); \ > - addr; \ > -}) > -#endif > - > #endif /* __ASM_COMPILER_H */ Acked-by: Will Deacon <will@kernel.org> Will ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH 3/3] arm64: Drop the inline assembly implementation of function_nocfi 2022-04-01 20:19 ` [PATCH 3/3] arm64: Drop the inline assembly implementation of function_nocfi Sami Tolvanen 2022-04-04 9:03 ` Will Deacon @ 2022-04-05 16:23 ` Mark Rutland 1 sibling, 0 replies; 12+ messages in thread From: Mark Rutland @ 2022-04-05 16:23 UTC (permalink / raw) To: Sami Tolvanen Cc: Kees Cook, Catalin Marinas, Masahiro Yamada, Nathan Chancellor, Nick Desaulniers, Will Deacon, linux-arm-kernel, linux-kernel, llvm On Fri, Apr 01, 2022 at 01:19:16PM -0700, Sami Tolvanen wrote: > Drop the inline assembly version of function_nocfi() now that > CONFIG_CFI_CLANG depends on __builtin_function_start(), which allows > this macro to be implemented more cleanly and in a way that works also > with static initializers. > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > arch/arm64/include/asm/compiler.h | 16 ---------------- > 1 file changed, 16 deletions(-) It's very nice to see the asm go here! I grabbed the LLVM 14.0.0 binary release from llvm.org and gave this a spin. I tested with ThinLTO and CFI_CLANG, and verified that CPU hotplug and ftrace worked as expected (given those rely on function_nocfi()), and that the LKDTM CFI_FORWARD_PROTO caught the mismatched prototype as expected. FWIW: Reviewed-by: Mark Rutland <mark.rutland@arm.com> Tested-by: Mark Rutland <mark.rutland@arm.com> As noted on patch 2 I think we should squash the series together, but those tags apply either way. Thanks, Mark. > > diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h > index dc3ea4080e2e..6fb2e6bcc392 100644 > --- a/arch/arm64/include/asm/compiler.h > +++ b/arch/arm64/include/asm/compiler.h > @@ -23,20 +23,4 @@ > #define __builtin_return_address(val) \ > (void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val))) > > -#ifdef CONFIG_CFI_CLANG > -/* > - * With CONFIG_CFI_CLANG, the compiler replaces function address > - * references with the address of the function's CFI jump table > - * entry. The function_nocfi macro always returns the address of the > - * actual function instead. > - */ > -#define function_nocfi(x) ({ \ > - void *addr; \ > - asm("adrp %0, " __stringify(x) "\n\t" \ > - "add %0, %0, :lo12:" __stringify(x) \ > - : "=r" (addr)); \ > - addr; \ > -}) > -#endif > - > #endif /* __ASM_COMPILER_H */ > -- > 2.35.0 > ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH 0/3] cfi: Use __builtin_function_start 2022-04-01 20:19 [PATCH 0/3] cfi: Use __builtin_function_start Sami Tolvanen ` (2 preceding siblings ...) 2022-04-01 20:19 ` [PATCH 3/3] arm64: Drop the inline assembly implementation of function_nocfi Sami Tolvanen @ 2022-04-01 20:49 ` Nick Desaulniers 3 siblings, 0 replies; 12+ messages in thread From: Nick Desaulniers @ 2022-04-01 20:49 UTC (permalink / raw) To: Sami Tolvanen Cc: Kees Cook, Catalin Marinas, Mark Rutland, Masahiro Yamada, Nathan Chancellor, Will Deacon, linux-arm-kernel, linux-kernel, llvm On Fri, Apr 1, 2022 at 1:19 PM Sami Tolvanen <samitolvanen@google.com> wrote: > > Clang 14 introduced the __builtin_function_start intrinsic, which > makes it possible to cleanly implement the function_nocfi() macro in a > way that also works with static initializers. Add a default > function_nocfi() implementation and drop the arm64 inline assembly > version. For the series Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> I wouldn't mind if patch 1/3 included a link to the llvm commit in the commit message. Link: https://github.com/llvm/llvm-project/commit/ec2e26eaf63558934f5b73a6e530edc453cf9508 Link: https://github.com/ClangBuiltLinux/linux/issues/1353 > > Sami Tolvanen (3): > kbuild: Change CFI_CLANG to depend on __builtin_function_start > linux/compiler-clang.h: define function_nocfi > arm64: Drop the inline assembly implementation of function_nocfi > > arch/Kconfig | 5 +---- > arch/arm64/include/asm/compiler.h | 16 ---------------- > include/linux/compiler-clang.h | 10 ++++++++++ > init/Kconfig | 3 +++ > 4 files changed, 14 insertions(+), 20 deletions(-) > > -- > 2.35.0 > -- Thanks, ~Nick Desaulniers ^ permalink raw reply [flat|nested] 12+ messages in thread
end of thread, other threads:[~2022-04-06 0:21 UTC | newest] Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-04-01 20:19 [PATCH 0/3] cfi: Use __builtin_function_start Sami Tolvanen 2022-04-01 20:19 ` [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start Sami Tolvanen 2022-04-02 13:31 ` Masahiro Yamada 2022-04-04 19:40 ` Sami Tolvanen 2022-04-04 22:52 ` Nathan Chancellor 2022-04-05 2:53 ` Kees Cook 2022-04-01 20:19 ` [PATCH 2/3] linux/compiler-clang.h: define function_nocfi Sami Tolvanen 2022-04-05 16:16 ` Mark Rutland 2022-04-01 20:19 ` [PATCH 3/3] arm64: Drop the inline assembly implementation of function_nocfi Sami Tolvanen 2022-04-04 9:03 ` Will Deacon 2022-04-05 16:23 ` Mark Rutland 2022-04-01 20:49 ` [PATCH 0/3] cfi: Use __builtin_function_start Nick Desaulniers
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