Re: [PATCH v4 5/7] powerpc/64s: Un-blacklist system_call() from kprobes
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2017-06-29 10:55:45
On Thu, 29 Jun 2017 16:11:08 +0530 "Naveen N. Rao" [off-list ref] wrote:
It is actually safe to probe system_call() in entry_64.S, but only till we unset MSR_RI. To allow this, add a new symbol system_call_exit() after the mtmsrd and blacklist that. Though the mtmsrd instruction itself is now whitelisted, we won't be allowed to probe on it as we don't allow probing on rfi and mtmsr instructions (checked for in arch_prepare_kprobe()).
Can you perhaps add a small comment to explain the label (and why it's safe to have after the mtmsrd). It could be a bit confusing to read if you don't have that detail of the tracer in your mind. Other than that Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
quoted hunk ↗ jump to hunk
Suggested-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Naveen N. Rao <redacted> --- arch/powerpc/kernel/entry_64.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index c39436706555..7a87427a67cd 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S@@ -205,6 +205,7 @@ system_call: /* label this so stack traces look sane */ mtmsrd r11,1 #endif /* CONFIG_PPC_BOOK3E */ +system_call_exit: ld r9,TI_FLAGS(r12) li r11,-MAX_ERRNO andi. r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)@@ -413,7 +414,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) b . /* prevent speculative execution */ #endif _ASM_NOKPROBE_SYMBOL(system_call_common); -_ASM_NOKPROBE_SYMBOL(system_call); +_ASM_NOKPROBE_SYMBOL(system_call_exit); /* Save non-volatile GPRs, if not already saved. */ _GLOBAL(save_nvgprs)