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powerpc/perf: Dereference BHRB entries safely 

It's theoretically possible that branch instructions recorded in
BHRB (Branch History Rolling Buffer) entries have already been
unmapped before they are processed by the kernel. Hence, trying to
dereference such memory location will result in a crash. eg:

    Unable to handle kernel paging request for data at address 0xd000000019c41764
    Faulting instruction address: 0xc000000000084a14
    NIP [c000000000084a14] branch_target+0x4/0x70
    LR [c0000000000eb828] record_and_restart+0x568/0x5c0
    Call Trace:
    [c0000000000eb3b4] record_and_restart+0xf4/0x5c0 (unreliable)
    [c0000000000ec378] perf_event_interrupt+0x298/0x460
    [c000000000027964] performance_monitor_exception+0x54/0x70
    [c000000000009ba4] performance_monitor_common+0x114/0x120

Fix it by deferefencing the addresses safely.

Fixes: 691231846c ("powerpc/perf: Fix setting of "to" addresses for BHRB")
Cc: stable@vger.kernel.org # v3.10+
Suggested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
[mpe: Use probe_kernel_read() which is clearer, tweak change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Ravi Bangoria 2017-12-12 17:59:15 +05:30 committed by Michael Ellerman
parent d810418208
commit f41d84dddc
1 changed files with 6 additions and 2 deletions
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8
arch/powerpc/perf/core-book3s.c
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@ -410,8 +410,12 @@ static __u64 power_pmu_bhrb_to(u64 addr)
int ret;
__u64 target;
if (is_kernel_addr(addr))
return branch_target((unsigned int *)addr);
if (is_kernel_addr(addr)) {
if (probe_kernel_read(&instr, (void *)addr, sizeof(instr)))
return 0;
return branch_target(&instr);
}
/* Userspace: need copy instruction here then translate it */
pagefault_disable();