On Thu, Apr 17, 2025 at 12:42:27AM +0530, Hari Bathini wrote:
> While r15 is clobbered always with PPC_FTRACE_OUT_OF_LINE, it is
> not restored in livepatch sequence leading to not so obvious fails
> like below:
>
> BUG: Unable to handle kernel data access on write at 0xc0000000000f9078
> Faulting instruction address: 0xc0000000018ff958
> Oops: Kernel access of bad area, sig: 11 [#1]
> ...
> NIP: c0000000018ff958 LR: c0000000018ff930 CTR: c0000000009c0790
> REGS: c00000005f2e7790 TRAP: 0300 Tainted: G K (6.14.0+)
> MSR: 8000000000009033 <SF,EE,ME,IR,DR,RI,LE> CR: 2822880b XER: 20040000
> CFAR: c0000000008addc0 DAR: c0000000000f9078 DSISR: 0a000000 IRQMASK: 1
> GPR00: c0000000018f2584 c00000005f2e7a30 c00000000280a900 c000000017ffa488
> GPR04: 0000000000000008 0000000000000000 c0000000018f24fc 000000000000000d
> GPR08: fffffffffffe0000 000000000000000d 0000000000000000 0000000000008000
> GPR12: c0000000009c0790 c000000017ffa480 c00000005f2e7c78 c0000000000f9070
> GPR16: c00000005f2e7c90 0000000000000000 0000000000000000 0000000000000000
> GPR20: 0000000000000000 c00000005f3efa80 c00000005f2e7c60 c00000005f2e7c88
> GPR24: c00000005f2e7c60 0000000000000001 c0000000000f9078 0000000000000000
> GPR28: 00007fff97960000 c000000017ffa480 0000000000000000 c0000000000f9078
> ...
> Call Trace:
> check_heap_object+0x34/0x390 (unreliable)
> __mutex_unlock_slowpath.isra.0+0xe4/0x230
> seq_read_iter+0x430/0xa90
> proc_reg_read_iter+0xa4/0x200
> vfs_read+0x41c/0x510
> ksys_read+0xa4/0x190
> system_call_exception+0x1d0/0x440
> system_call_vectored_common+0x15c/0x2ec
>
> Fix it by restoring r15 always.
>
> Fixes: eec37961a56a ("powerpc64/ftrace: Move ftrace sequence out of line")
> Reported-by: Viktor Malik <vma...@redhat.com>
> Closes:
> https://lore.kernel.org/lkml/1aec4a9a-a30b-43fd-b303-7a351caec...@redhat.com
> Cc: sta...@vger.kernel.org # v6.13+
> Signed-off-by: Hari Bathini <hbath...@linux.ibm.com>
> ---
> arch/powerpc/kernel/trace/ftrace_entry.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S
> b/arch/powerpc/kernel/trace/ftrace_entry.S
> index 2c1b24100eca..3565c67fc638 100644
> --- a/arch/powerpc/kernel/trace/ftrace_entry.S
> +++ b/arch/powerpc/kernel/trace/ftrace_entry.S
> @@ -212,10 +212,10 @@
> bne- 1f
>
> mr r3, r15
> +1: mtlr r3
> .if \allregs == 0
> REST_GPR(15, r1)
> .endif
> -1: mtlr r3
> #endif
LGTM.
Acked-by: Naveen N Rao (AMD) <nav...@kernel.org>
- Naveen
