| Message ID | 20211005123645.2766258-1-sumit.garg@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] arm64: ftrace: use function_nocfi for _mcount as well | expand |
Hi Sumit, On Tue, Oct 5, 2021 at 5:37 AM Sumit Garg <sumit.garg@linaro.org> wrote: > > Commit 800618f955a9 ("arm64: ftrace: use function_nocfi for ftrace_call") > only fixed address of ftrace_call but address of _mcount needs to be > fixed as well. Use function_nocfi() to get the actual address of _mcount > function as with CONFIG_CFI_CLANG, the compiler replaces function pointers > with jump table addresses which breaks dynamic ftrace as the address of > _mcount is replaced with the address of _mcount.cfi_jt. > > This problem won't apply where the toolchain implements > -fpatchable-function-entry as we'll use that in preference to regular -pg, > i.e. this won't show up with recent versions of clang. > > Fixes: 9186ad8e66bab6a1 ("arm64: allow CONFIG_CFI_CLANG to be selected") > Signed-off-by: Sumit Garg <sumit.garg@linaro.org> > Acked-by: Mark Rutland <mark.rutland@arm.com> > --- > > Changes in v2: > - Added fixes tag. > - Extended commit description. > - Picked up Mark's ack. > > arch/arm64/include/asm/ftrace.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > index 91fa4baa1a93..347b0cc68f07 100644 > --- a/arch/arm64/include/asm/ftrace.h > +++ b/arch/arm64/include/asm/ftrace.h > @@ -15,7 +15,7 @@ > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > #define ARCH_SUPPORTS_FTRACE_OPS 1 > #else > -#define MCOUNT_ADDR ((unsigned long)_mcount) > +#define MCOUNT_ADDR ((unsigned long)function_nocfi(_mcount)) > #endif > > /* The BL at the callsite's adjusted rec->ip */ > -- > 2.17.1 > Clang >= 10 supports -fpatchable-function-entry and CFI requires Clang 12, so I assume this is only an issue if CONFIG_DYNAMIC_FTRACE_WITH_REGS is explicitly disabled? Nevertheless, the patch looks good to me. Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Sami
On Tue, Oct 05, 2021 at 08:20:02AM -0700, Sami Tolvanen wrote: > Hi Sumit, > > On Tue, Oct 5, 2021 at 5:37 AM Sumit Garg <sumit.garg@linaro.org> wrote: > > > > Commit 800618f955a9 ("arm64: ftrace: use function_nocfi for ftrace_call") > > only fixed address of ftrace_call but address of _mcount needs to be > > fixed as well. Use function_nocfi() to get the actual address of _mcount > > function as with CONFIG_CFI_CLANG, the compiler replaces function pointers > > with jump table addresses which breaks dynamic ftrace as the address of > > _mcount is replaced with the address of _mcount.cfi_jt. > > > > This problem won't apply where the toolchain implements > > -fpatchable-function-entry as we'll use that in preference to regular -pg, > > i.e. this won't show up with recent versions of clang. > > > > Fixes: 9186ad8e66bab6a1 ("arm64: allow CONFIG_CFI_CLANG to be selected") > > Signed-off-by: Sumit Garg <sumit.garg@linaro.org> > > Acked-by: Mark Rutland <mark.rutland@arm.com> > > --- > > > > Changes in v2: > > - Added fixes tag. > > - Extended commit description. > > - Picked up Mark's ack. > > > > arch/arm64/include/asm/ftrace.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > > index 91fa4baa1a93..347b0cc68f07 100644 > > --- a/arch/arm64/include/asm/ftrace.h > > +++ b/arch/arm64/include/asm/ftrace.h > > @@ -15,7 +15,7 @@ > > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > #define ARCH_SUPPORTS_FTRACE_OPS 1 > > #else > > -#define MCOUNT_ADDR ((unsigned long)_mcount) > > +#define MCOUNT_ADDR ((unsigned long)function_nocfi(_mcount)) > > #endif > > > > /* The BL at the callsite's adjusted rec->ip */ > > -- > > 2.17.1 > > > > Clang >= 10 supports -fpatchable-function-entry and CFI requires Clang > 12, so I assume this is only an issue if > CONFIG_DYNAMIC_FTRACE_WITH_REGS is explicitly disabled? I don't believe it's possible to disable explicitly, since DYNAMIC_FTRACE_WITH_REGS isn't user selectable, and is def bool y, depending on HAVE_DYNAMIC_FTRACE_WITH_REGS. Sumit, have you actually seen a problem, or was this found by inspection? If this isn't an issue in practice, we could add the funciton_nocfi() for consistency, but we should make that clear in the commit message, and drop the fixes tag. Thanks, Mark.
Hi Mark, Sami, On Tue, 5 Oct 2021 at 21:05, Mark Rutland <mark.rutland@arm.com> wrote: > > On Tue, Oct 05, 2021 at 08:20:02AM -0700, Sami Tolvanen wrote: > > Hi Sumit, > > > > On Tue, Oct 5, 2021 at 5:37 AM Sumit Garg <sumit.garg@linaro.org> wrote: > > > > > > Commit 800618f955a9 ("arm64: ftrace: use function_nocfi for ftrace_call") > > > only fixed address of ftrace_call but address of _mcount needs to be > > > fixed as well. Use function_nocfi() to get the actual address of _mcount > > > function as with CONFIG_CFI_CLANG, the compiler replaces function pointers > > > with jump table addresses which breaks dynamic ftrace as the address of > > > _mcount is replaced with the address of _mcount.cfi_jt. > > > > > > This problem won't apply where the toolchain implements > > > -fpatchable-function-entry as we'll use that in preference to regular -pg, > > > i.e. this won't show up with recent versions of clang. > > > > > > Fixes: 9186ad8e66bab6a1 ("arm64: allow CONFIG_CFI_CLANG to be selected") > > > Signed-off-by: Sumit Garg <sumit.garg@linaro.org> > > > Acked-by: Mark Rutland <mark.rutland@arm.com> > > > --- > > > > > > Changes in v2: > > > - Added fixes tag. > > > - Extended commit description. > > > - Picked up Mark's ack. > > > > > > arch/arm64/include/asm/ftrace.h | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > > > index 91fa4baa1a93..347b0cc68f07 100644 > > > --- a/arch/arm64/include/asm/ftrace.h > > > +++ b/arch/arm64/include/asm/ftrace.h > > > @@ -15,7 +15,7 @@ > > > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > > #define ARCH_SUPPORTS_FTRACE_OPS 1 > > > #else > > > -#define MCOUNT_ADDR ((unsigned long)_mcount) > > > +#define MCOUNT_ADDR ((unsigned long)function_nocfi(_mcount)) > > > #endif > > > > > > /* The BL at the callsite's adjusted rec->ip */ > > > -- > > > 2.17.1 > > > > > > > Clang >= 10 supports -fpatchable-function-entry and CFI requires Clang > > 12, so I assume this is only an issue if > > CONFIG_DYNAMIC_FTRACE_WITH_REGS is explicitly disabled? > > I don't believe it's possible to disable explicitly, since > DYNAMIC_FTRACE_WITH_REGS isn't user selectable, and is def bool y, > depending on HAVE_DYNAMIC_FTRACE_WITH_REGS. > Ah, I see. > Sumit, have you actually seen a problem, or was this found by > inspection? > Actually I have seen this ftrace problem with the android11-5.4-lts kernel and AOSP master user-space on db845c. The reason being kernel v5.4 LTS doesn't support ftrace with -fpatchable-function-entry on arm64. With the mainline, I haven't tried to reproduce this issue but it was rather by inspection that this needs to be fixed as well. > If this isn't an issue in practice, we could add the funciton_nocfi() > for consistency, but we should make that clear in the commit message, > and drop the fixes tag. Sure, let me drop the fixes tag and update the commit description in v3 as mainline only enabled CFI_CLANG for arm64 when "-fpatchable-function-entry" is supported. -Sumit > > Thanks, > Mark.
Hi Sumit, On Wed, Oct 06, 2021 at 11:05:52AM +0530, Sumit Garg wrote: > On Tue, 5 Oct 2021 at 21:05, Mark Rutland <mark.rutland@arm.com> wrote: > > On Tue, Oct 05, 2021 at 08:20:02AM -0700, Sami Tolvanen wrote: > > > On Tue, Oct 5, 2021 at 5:37 AM Sumit Garg <sumit.garg@linaro.org> wrote: > > > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > > > > index 91fa4baa1a93..347b0cc68f07 100644 > > > > --- a/arch/arm64/include/asm/ftrace.h > > > > +++ b/arch/arm64/include/asm/ftrace.h > > > > @@ -15,7 +15,7 @@ > > > > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > > > #define ARCH_SUPPORTS_FTRACE_OPS 1 > > > > #else > > > > -#define MCOUNT_ADDR ((unsigned long)_mcount) > > > > +#define MCOUNT_ADDR ((unsigned long)function_nocfi(_mcount)) > > > > #endif > > > > > > > > /* The BL at the callsite's adjusted rec->ip */ > > > > -- > > > > 2.17.1 > > > > > > > > > > Clang >= 10 supports -fpatchable-function-entry and CFI requires Clang > > > 12, so I assume this is only an issue if > > > CONFIG_DYNAMIC_FTRACE_WITH_REGS is explicitly disabled? > > > > I don't believe it's possible to disable explicitly, since > > DYNAMIC_FTRACE_WITH_REGS isn't user selectable, and is def bool y, > > depending on HAVE_DYNAMIC_FTRACE_WITH_REGS. > > > > Ah, I see. > > > Sumit, have you actually seen a problem, or was this found by > > inspection? > > > > Actually I have seen this ftrace problem with the android11-5.4-lts > kernel and AOSP master user-space on db845c. The reason being kernel > v5.4 LTS doesn't support ftrace with -fpatchable-function-entry on > arm64. > > With the mainline, I haven't tried to reproduce this issue but it was > rather by inspection that this needs to be fixed as well. > > > If this isn't an issue in practice, we could add the funciton_nocfi() > > for consistency, but we should make that clear in the commit message, > > and drop the fixes tag. > > Sure, let me drop the fixes tag and update the commit description in > v3 as mainline only enabled CFI_CLANG for arm64 when > "-fpatchable-function-entry" is supported. Did you post a v3? Just want to make sure I didn't miss it. Will
Hi Will, On Fri, 8 Oct 2021 at 13:35, Will Deacon <will@kernel.org> wrote: > > Hi Sumit, > > On Wed, Oct 06, 2021 at 11:05:52AM +0530, Sumit Garg wrote: > > On Tue, 5 Oct 2021 at 21:05, Mark Rutland <mark.rutland@arm.com> wrote: > > > On Tue, Oct 05, 2021 at 08:20:02AM -0700, Sami Tolvanen wrote: > > > > On Tue, Oct 5, 2021 at 5:37 AM Sumit Garg <sumit.garg@linaro.org> wrote: > > > > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > > > > > index 91fa4baa1a93..347b0cc68f07 100644 > > > > > --- a/arch/arm64/include/asm/ftrace.h > > > > > +++ b/arch/arm64/include/asm/ftrace.h > > > > > @@ -15,7 +15,7 @@ > > > > > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > > > > #define ARCH_SUPPORTS_FTRACE_OPS 1 > > > > > #else > > > > > -#define MCOUNT_ADDR ((unsigned long)_mcount) > > > > > +#define MCOUNT_ADDR ((unsigned long)function_nocfi(_mcount)) > > > > > #endif > > > > > > > > > > /* The BL at the callsite's adjusted rec->ip */ > > > > > -- > > > > > 2.17.1 > > > > > > > > > > > > > Clang >= 10 supports -fpatchable-function-entry and CFI requires Clang > > > > 12, so I assume this is only an issue if > > > > CONFIG_DYNAMIC_FTRACE_WITH_REGS is explicitly disabled? > > > > > > I don't believe it's possible to disable explicitly, since > > > DYNAMIC_FTRACE_WITH_REGS isn't user selectable, and is def bool y, > > > depending on HAVE_DYNAMIC_FTRACE_WITH_REGS. > > > > > > > Ah, I see. > > > > > Sumit, have you actually seen a problem, or was this found by > > > inspection? > > > > > > > Actually I have seen this ftrace problem with the android11-5.4-lts > > kernel and AOSP master user-space on db845c. The reason being kernel > > v5.4 LTS doesn't support ftrace with -fpatchable-function-entry on > > arm64. > > > > With the mainline, I haven't tried to reproduce this issue but it was > > rather by inspection that this needs to be fixed as well. > > > > > If this isn't an issue in practice, we could add the funciton_nocfi() > > > for consistency, but we should make that clear in the commit message, > > > and drop the fixes tag. > > > > Sure, let me drop the fixes tag and update the commit description in > > v3 as mainline only enabled CFI_CLANG for arm64 when > > "-fpatchable-function-entry" is supported. > > Did you post a v3? Just want to make sure I didn't miss it. > Apologies for the delay, here [1] it is. [1] https://lkml.org/lkml/2021/10/11/485 -Sumit > Will
diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h index 91fa4baa1a93..347b0cc68f07 100644 --- a/arch/arm64/include/asm/ftrace.h +++ b/arch/arm64/include/asm/ftrace.h @@ -15,7 +15,7 @@ #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS #define ARCH_SUPPORTS_FTRACE_OPS 1 #else -#define MCOUNT_ADDR ((unsigned long)_mcount) +#define MCOUNT_ADDR ((unsigned long)function_nocfi(_mcount)) #endif /* The BL at the callsite's adjusted rec->ip */
Commit 800618f955a9 ("arm64: ftrace: use function_nocfi for ftrace_call") only fixed address of ftrace_call but address of _mcount needs to be fixed as well. Use function_nocfi() to get the actual address of _mcount function as with CONFIG_CFI_CLANG, the compiler replaces function pointers with jump table addresses which breaks dynamic ftrace as the address of _mcount is replaced with the address of _mcount.cfi_jt. This problem won't apply where the toolchain implements -fpatchable-function-entry as we'll use that in preference to regular -pg, i.e. this won't show up with recent versions of clang. Fixes: 9186ad8e66bab6a1 ("arm64: allow CONFIG_CFI_CLANG to be selected") Signed-off-by: Sumit Garg <sumit.garg@linaro.org> Acked-by: Mark Rutland <mark.rutland@arm.com> --- Changes in v2: - Added fixes tag. - Extended commit description. - Picked up Mark's ack. arch/arm64/include/asm/ftrace.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)