| From stable+bounces-6799-greg=kroah.com@vger.kernel.org Fri Dec 15 12:15:27 2023 |
| From: Naveen N Rao <naveen@kernel.org> |
| Date: Fri, 15 Dec 2023 16:41:21 +0530 |
| Subject: powerpc/ftrace: Create a dummy stackframe to fix stack unwind |
| To: <stable@vger.kernel.org> |
| Cc: Greg KH <gregkh@linuxfoundation.org>, Michael Ellerman <mpe@ellerman.id.au> |
| Message-ID: <20231215111122.2361478-1-naveen@kernel.org> |
| |
| From: Naveen N Rao <naveen@kernel.org> |
| |
| commit 41a506ef71eb38d94fe133f565c87c3e06ccc072 upstream. |
| |
| With ppc64 -mprofile-kernel and ppc32 -pg, profiling instructions to |
| call into ftrace are emitted right at function entry. The instruction |
| sequence used is minimal to reduce overhead. Crucially, a stackframe is |
| not created for the function being traced. This breaks stack unwinding |
| since the function being traced does not have a stackframe for itself. |
| As such, it never shows up in the backtrace: |
| |
| /sys/kernel/debug/tracing # echo 1 > /proc/sys/kernel/stack_tracer_enabled |
| /sys/kernel/debug/tracing # cat stack_trace |
| Depth Size Location (17 entries) |
| ----- ---- -------- |
| 0) 4144 32 ftrace_call+0x4/0x44 |
| 1) 4112 432 get_page_from_freelist+0x26c/0x1ad0 |
| 2) 3680 496 __alloc_pages+0x290/0x1280 |
| 3) 3184 336 __folio_alloc+0x34/0x90 |
| 4) 2848 176 vma_alloc_folio+0xd8/0x540 |
| 5) 2672 272 __handle_mm_fault+0x700/0x1cc0 |
| 6) 2400 208 handle_mm_fault+0xf0/0x3f0 |
| 7) 2192 80 ___do_page_fault+0x3e4/0xbe0 |
| 8) 2112 160 do_page_fault+0x30/0xc0 |
| 9) 1952 256 data_access_common_virt+0x210/0x220 |
| 10) 1696 400 0xc00000000f16b100 |
| 11) 1296 384 load_elf_binary+0x804/0x1b80 |
| 12) 912 208 bprm_execve+0x2d8/0x7e0 |
| 13) 704 64 do_execveat_common+0x1d0/0x2f0 |
| 14) 640 160 sys_execve+0x54/0x70 |
| 15) 480 64 system_call_exception+0x138/0x350 |
| 16) 416 416 system_call_common+0x160/0x2c4 |
| |
| Fix this by having ftrace create a dummy stackframe for the function |
| being traced. With this, backtraces now capture the function being |
| traced: |
| |
| /sys/kernel/debug/tracing # cat stack_trace |
| Depth Size Location (17 entries) |
| ----- ---- -------- |
| 0) 3888 32 _raw_spin_trylock+0x8/0x70 |
| 1) 3856 576 get_page_from_freelist+0x26c/0x1ad0 |
| 2) 3280 64 __alloc_pages+0x290/0x1280 |
| 3) 3216 336 __folio_alloc+0x34/0x90 |
| 4) 2880 176 vma_alloc_folio+0xd8/0x540 |
| 5) 2704 416 __handle_mm_fault+0x700/0x1cc0 |
| 6) 2288 96 handle_mm_fault+0xf0/0x3f0 |
| 7) 2192 48 ___do_page_fault+0x3e4/0xbe0 |
| 8) 2144 192 do_page_fault+0x30/0xc0 |
| 9) 1952 608 data_access_common_virt+0x210/0x220 |
| 10) 1344 16 0xc0000000334bbb50 |
| 11) 1328 416 load_elf_binary+0x804/0x1b80 |
| 12) 912 64 bprm_execve+0x2d8/0x7e0 |
| 13) 848 176 do_execveat_common+0x1d0/0x2f0 |
| 14) 672 192 sys_execve+0x54/0x70 |
| 15) 480 64 system_call_exception+0x138/0x350 |
| 16) 416 416 system_call_common+0x160/0x2c4 |
| |
| This results in two additional stores in the ftrace entry code, but |
| produces reliable backtraces. |
| |
| Fixes: 153086644fd1 ("powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI") |
| Cc: stable@vger.kernel.org |
| Signed-off-by: Naveen N Rao <naveen@kernel.org> |
| Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
| Link: https://msgid.link/20230621051349.759567-1-naveen@kernel.org |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| arch/powerpc/kernel/trace/ftrace_64_mprofile.S | 7 ++++++- |
| 1 file changed, 6 insertions(+), 1 deletion(-) |
| |
| --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S |
| +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S |
| @@ -41,6 +41,9 @@ _GLOBAL(ftrace_caller) |
| /* Save the original return address in A's stack frame */ |
| std r0,LRSAVE(r1) |
| |
| + /* Create a minimal stack frame for representing B */ |
| + stdu r1, -STACK_FRAME_MIN_SIZE(r1) |
| + |
| /* Create our stack frame + pt_regs */ |
| stdu r1,-SWITCH_FRAME_SIZE(r1) |
| |
| @@ -64,6 +67,8 @@ _GLOBAL(ftrace_caller) |
| mflr r7 |
| /* Save it as pt_regs->nip */ |
| std r7, _NIP(r1) |
| + /* Also save it in B's stackframe header for proper unwind */ |
| + std r7, LRSAVE+SWITCH_FRAME_SIZE(r1) |
| /* Save the read LR in pt_regs->link */ |
| std r0, _LINK(r1) |
| |
| @@ -146,7 +151,7 @@ ftrace_call: |
| ld r2, 24(r1) |
| |
| /* Pop our stack frame */ |
| - addi r1, r1, SWITCH_FRAME_SIZE |
| + addi r1, r1, SWITCH_FRAME_SIZE+STACK_FRAME_MIN_SIZE |
| |
| #ifdef CONFIG_LIVEPATCH |
| /* |
