This is a note to let you know that I've just added the patch titled powerpc/perf: Dereference BHRB entries safely to the 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: powerpc-perf-dereference-bhrb-entries-safely.patch and it can be found in the queue-3.18 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From f41d84dddc66b164ac16acf3f584c276146f1c48 Mon Sep 17 00:00:00 2001 From: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx> Date: Tue, 12 Dec 2017 17:59:15 +0530 Subject: powerpc/perf: Dereference BHRB entries safely From: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx> commit f41d84dddc66b164ac16acf3f584c276146f1c48 upstream. 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: 691231846ceb ("powerpc/perf: Fix setting of "to" addresses for BHRB") Suggested-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx> Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx> Reviewed-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx> [mpe: Use probe_kernel_read() which is clearer, tweak change log] Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/powerpc/perf/core-book3s.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -396,8 +396,12 @@ 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(); Patches currently in stable-queue which might be from ravi.bangoria@xxxxxxxxxxxxxxxxxx are queue-3.18/powerpc-perf-dereference-bhrb-entries-safely.patch