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    Subject[PATCH 4.15 18/72] powerpc/64s: Fix i-side SLB miss bad address handler saving nonvolatile GPRs
    Date
    4.15-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Nicholas Piggin <npiggin@gmail.com>

    commit 52396500f97c53860164debc7d4f759077853423 upstream.

    The SLB bad address handler's trap number fixup does not preserve the
    low bit that indicates nonvolatile GPRs have not been saved. This
    leads save_nvgprs to skip saving them, and subsequent functions and
    return from interrupt will think they are saved.

    This causes kernel branch-to-garbage debugging to not have correct
    registers, can also cause userspace to have its registers clobbered
    after a segfault.

    Fixes: f0f558b131db ("powerpc/mm: Preserve CFAR value on SLB miss caused by access to bogus address")
    Cc: stable@vger.kernel.org # v4.9+
    Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/powerpc/kernel/exceptions-64s.S | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/powerpc/kernel/exceptions-64s.S
    +++ b/arch/powerpc/kernel/exceptions-64s.S
    @@ -706,7 +706,7 @@ EXC_COMMON_BEGIN(bad_addr_slb)
    ld r3, PACA_EXSLB+EX_DAR(r13)
    std r3, _DAR(r1)
    beq cr6, 2f
    - li r10, 0x480 /* fix trap number for I-SLB miss */
    + li r10, 0x481 /* fix trap number for I-SLB miss */
    std r10, _TRAP(r1)
    2: bl save_nvgprs
    addi r3, r1, STACK_FRAME_OVERHEAD

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