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    Subject[PATCH 5.5 242/257] powerpc/kprobes: Ignore traps that happened in real mode
    Date
    From: Christophe Leroy <christophe.leroy@c-s.fr>

    commit 21f8b2fa3ca5b01f7a2b51b89ce97a3705a15aa0 upstream.

    When a program check exception happens while MMU translation is
    disabled, following Oops happens in kprobe_handler() in the following
    code:

    } else if (*addr != BREAKPOINT_INSTRUCTION) {

    BUG: Unable to handle kernel data access on read at 0x0000e268
    Faulting instruction address: 0xc000ec34
    Oops: Kernel access of bad area, sig: 11 [#1]
    BE PAGE_SIZE=16K PREEMPT CMPC885
    Modules linked in:
    CPU: 0 PID: 429 Comm: cat Not tainted 5.6.0-rc1-s3k-dev-00824-g84195dc6c58a #3267
    NIP: c000ec34 LR: c000ecd8 CTR: c019cab8
    REGS: ca4d3b58 TRAP: 0300 Not tainted (5.6.0-rc1-s3k-dev-00824-g84195dc6c58a)
    MSR: 00001032 <ME,IR,DR,RI> CR: 2a4d3c52 XER: 00000000
    DAR: 0000e268 DSISR: c0000000
    GPR00: c000b09c ca4d3c10 c66d0620 00000000 ca4d3c60 00000000 00009032 00000000
    GPR08: 00020000 00000000 c087de44 c000afe0 c66d0ad0 100d3dd6 fffffff3 00000000
    GPR16: 00000000 00000041 00000000 ca4d3d70 00000000 00000000 0000416d 00000000
    GPR24: 00000004 c53b6128 00000000 0000e268 00000000 c07c0000 c07bb6fc ca4d3c60
    NIP [c000ec34] kprobe_handler+0x128/0x290
    LR [c000ecd8] kprobe_handler+0x1cc/0x290
    Call Trace:
    [ca4d3c30] [c000b09c] program_check_exception+0xbc/0x6fc
    [ca4d3c50] [c000e43c] ret_from_except_full+0x0/0x4
    --- interrupt: 700 at 0xe268
    Instruction dump:
    913e0008 81220000 38600001 3929ffff 91220000 80010024 bb410008 7c0803a6
    38210020 4e800020 38600000 4e800020 <813b0000> 6d2a7fe0 2f8a0008 419e0154
    ---[ end trace 5b9152d4cdadd06d ]---

    kprobe is not prepared to handle events in real mode and functions
    running in real mode should have been blacklisted, so kprobe_handler()
    can safely bail out telling 'this trap is not mine' for any trap that
    happened while in real-mode.

    If the trap happened with MSR_IR or MSR_DR cleared, return 0
    immediately.

    Reported-by: Larry Finger <Larry.Finger@lwfinger.net>
    Fixes: 6cc89bad60a6 ("powerpc/kprobes: Invoke handlers directly")
    Cc: stable@vger.kernel.org # v4.10+
    Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
    Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
    Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/424331e2006e7291a1bfe40e7f3fa58825f565e1.1582054578.git.christophe.leroy@c-s.fr
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/powerpc/kernel/kprobes.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/arch/powerpc/kernel/kprobes.c
    +++ b/arch/powerpc/kernel/kprobes.c
    @@ -264,6 +264,9 @@ int kprobe_handler(struct pt_regs *regs)
    if (user_mode(regs))
    return 0;

    + if (!(regs->msr & MSR_IR) || !(regs->msr & MSR_DR))
    + return 0;
    +
    /*
    * We don't want to be preempted for the entire
    * duration of kprobe processing

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