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powerpc/64s: Un-blacklist system_call() from kprobes

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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.

Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Naveen N. Rao 2017-06-29 23:19:18 +05:30 committed by Michael Ellerman
parent 266de3a842
commit 3639d6619c
1 changed files with 13 additions and 1 deletions
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14
arch/powerpc/kernel/entry_64.S
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@ -188,6 +188,18 @@ system_call: /* label this so stack traces look sane */
andi. r10,r8,MSR_RI
beq- unrecov_restore
#endif
/*
* This is a few instructions into the actual syscall exit path (which actually
* starts at .Lsyscall_exit) to cater to kprobe blacklisting and to reduce the
* number of visible symbols for profiling purposes.
*
* We can probe from system_call until this point as MSR_RI is set. But once it
* is cleared below, we won't be able to take a trap.
*
* This is blacklisted from kprobes further below with _ASM_NOKPROBE_SYMBOL().
*/
system_call_exit:
/*
* Disable interrupts so current_thread_info()->flags can't change,
* and so that we don't get interrupted after loading SRR0/1.
@ -414,7 +426,7 @@ 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)