| From ccf886b107591ddfa3798949b38bcf4d4915890a Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Fri, 14 Sep 2018 13:10:04 +0930 |
| Subject: powerpc/vdso: Correct call frame information |
| |
| From: Alan Modra <amodra@gmail.com> |
| |
| [ Upstream commit 56d20861c027498b5a1112b4f9f05b56d906fdda ] |
| |
| Call Frame Information is used by gdb for back-traces and inserting |
| breakpoints on function return for the "finish" command. This failed |
| when inside __kernel_clock_gettime. More concerning than difficulty |
| debugging is that CFI is also used by stack frame unwinding code to |
| implement exceptions. If you have an app that needs to handle |
| asynchronous exceptions for some reason, and you are unlucky enough to |
| get one inside the VDSO time functions, your app will crash. |
| |
| What's wrong: There is control flow in __kernel_clock_gettime that |
| reaches label 99 without saving lr in r12. CFI info however is |
| interpreted by the unwinder without reference to control flow: It's a |
| simple matter of "Execute all the CFI opcodes up to the current |
| address". That means the unwinder thinks r12 contains the return |
| address at label 99. Disabuse it of that notion by resetting CFI for |
| the return address at label 99. |
| |
| Note that the ".cfi_restore lr" could have gone anywhere from the |
| "mtlr r12" a few instructions earlier to the instruction at label 99. |
| I put the CFI as late as possible, because in general that's best |
| practice (and if possible grouped with other CFI in order to reduce |
| the number of CFI opcodes executed when unwinding). Using r12 as the |
| return address is perfectly fine after the "mtlr r12" since r12 on |
| that code path still contains the return address. |
| |
| __get_datapage also has a CFI error. That function temporarily saves |
| lr in r0, and reflects that fact with ".cfi_register lr,r0". A later |
| use of r0 means the CFI at that point isn't correct, as r0 no longer |
| contains the return address. Fix that too. |
| |
| Signed-off-by: Alan Modra <amodra@gmail.com> |
| Tested-by: Reza Arbab <arbab@linux.ibm.com> |
| Signed-off-by: Paul Mackerras <paulus@ozlabs.org> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| arch/powerpc/kernel/vdso32/datapage.S | 1 + |
| arch/powerpc/kernel/vdso32/gettimeofday.S | 1 + |
| arch/powerpc/kernel/vdso64/datapage.S | 1 + |
| arch/powerpc/kernel/vdso64/gettimeofday.S | 1 + |
| 4 files changed, 4 insertions(+) |
| |
| diff --git a/arch/powerpc/kernel/vdso32/datapage.S b/arch/powerpc/kernel/vdso32/datapage.S |
| index 3745113fcc652..2a7eb5452aba7 100644 |
| --- a/arch/powerpc/kernel/vdso32/datapage.S |
| +++ b/arch/powerpc/kernel/vdso32/datapage.S |
| @@ -37,6 +37,7 @@ data_page_branch: |
| mtlr r0 |
| addi r3, r3, __kernel_datapage_offset-data_page_branch |
| lwz r0,0(r3) |
| + .cfi_restore lr |
| add r3,r0,r3 |
| blr |
| .cfi_endproc |
| diff --git a/arch/powerpc/kernel/vdso32/gettimeofday.S b/arch/powerpc/kernel/vdso32/gettimeofday.S |
| index 75cff3f336b3a..afd516b572f86 100644 |
| --- a/arch/powerpc/kernel/vdso32/gettimeofday.S |
| +++ b/arch/powerpc/kernel/vdso32/gettimeofday.S |
| @@ -139,6 +139,7 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime) |
| */ |
| 99: |
| li r0,__NR_clock_gettime |
| + .cfi_restore lr |
| sc |
| blr |
| .cfi_endproc |
| diff --git a/arch/powerpc/kernel/vdso64/datapage.S b/arch/powerpc/kernel/vdso64/datapage.S |
| index abf17feffe404..bf96686915116 100644 |
| --- a/arch/powerpc/kernel/vdso64/datapage.S |
| +++ b/arch/powerpc/kernel/vdso64/datapage.S |
| @@ -37,6 +37,7 @@ data_page_branch: |
| mtlr r0 |
| addi r3, r3, __kernel_datapage_offset-data_page_branch |
| lwz r0,0(r3) |
| + .cfi_restore lr |
| add r3,r0,r3 |
| blr |
| .cfi_endproc |
| diff --git a/arch/powerpc/kernel/vdso64/gettimeofday.S b/arch/powerpc/kernel/vdso64/gettimeofday.S |
| index afbad2ac31472..1f324c28705bc 100644 |
| --- a/arch/powerpc/kernel/vdso64/gettimeofday.S |
| +++ b/arch/powerpc/kernel/vdso64/gettimeofday.S |
| @@ -169,6 +169,7 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime) |
| */ |
| 99: |
| li r0,__NR_clock_gettime |
| + .cfi_restore lr |
| sc |
| blr |
| .cfi_endproc |
| -- |
| 2.20.1 |
| |