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    Subject[PATCH 4.19 32/58] arm64: kgdb: Fix single-step exception handling oops
    Date
    From: Wei Li <liwei391@huawei.com>

    [ Upstream commit 8523c006264df65aac7d77284cc69aac46a6f842 ]

    After entering kdb due to breakpoint, when we execute 'ss' or 'go' (will
    delay installing breakpoints, do single-step first), it won't work
    correctly, and it will enter kdb due to oops.

    It's because the reason gotten in kdb_stub() is not as expected, and it
    seems that the ex_vector for single-step should be 0, like what arch
    powerpc/sh/parisc has implemented.

    Before the patch:
    Entering kdb (current=0xffff8000119e2dc0, pid 0) on processor 0 due to Keyboard Entry
    [0]kdb> bp printk
    Instruction(i) BP #0 at 0xffff8000101486cc (printk)
    is enabled addr at ffff8000101486cc, hardtype=0 installed=0

    [0]kdb> g

    / # echo h > /proc/sysrq-trigger

    Entering kdb (current=0xffff0000fa878040, pid 266) on processor 3 due to Breakpoint @ 0xffff8000101486cc
    [3]kdb> ss

    Entering kdb (current=0xffff0000fa878040, pid 266) on processor 3 Oops: (null)
    due to oops @ 0xffff800010082ab8
    CPU: 3 PID: 266 Comm: sh Not tainted 5.7.0-rc4-13839-gf0e5ad491718 #6
    Hardware name: linux,dummy-virt (DT)
    pstate: 00000085 (nzcv daIf -PAN -UAO)
    pc : el1_irq+0x78/0x180
    lr : __handle_sysrq+0x80/0x190
    sp : ffff800015003bf0
    x29: ffff800015003d20 x28: ffff0000fa878040
    x27: 0000000000000000 x26: ffff80001126b1f0
    x25: ffff800011b6a0d8 x24: 0000000000000000
    x23: 0000000080200005 x22: ffff8000101486cc
    x21: ffff800015003d30 x20: 0000ffffffffffff
    x19: ffff8000119f2000 x18: 0000000000000000
    x17: 0000000000000000 x16: 0000000000000000
    x15: 0000000000000000 x14: 0000000000000000
    x13: 0000000000000000 x12: 0000000000000000
    x11: 0000000000000000 x10: 0000000000000000
    x9 : 0000000000000000 x8 : ffff800015003e50
    x7 : 0000000000000002 x6 : 00000000380b9990
    x5 : ffff8000106e99e8 x4 : ffff0000fadd83c0
    x3 : 0000ffffffffffff x2 : ffff800011b6a0d8
    x1 : ffff800011b6a000 x0 : ffff80001130c9d8
    Call trace:
    el1_irq+0x78/0x180
    printk+0x0/0x84
    write_sysrq_trigger+0xb0/0x118
    proc_reg_write+0xb4/0xe0
    __vfs_write+0x18/0x40
    vfs_write+0xb0/0x1b8
    ksys_write+0x64/0xf0
    __arm64_sys_write+0x14/0x20
    el0_svc_common.constprop.2+0xb0/0x168
    do_el0_svc+0x20/0x98
    el0_sync_handler+0xec/0x1a8
    el0_sync+0x140/0x180

    [3]kdb>

    After the patch:
    Entering kdb (current=0xffff8000119e2dc0, pid 0) on processor 0 due to Keyboard Entry
    [0]kdb> bp printk
    Instruction(i) BP #0 at 0xffff8000101486cc (printk)
    is enabled addr at ffff8000101486cc, hardtype=0 installed=0

    [0]kdb> g

    / # echo h > /proc/sysrq-trigger

    Entering kdb (current=0xffff0000fa852bc0, pid 268) on processor 0 due to Breakpoint @ 0xffff8000101486cc
    [0]kdb> g

    Entering kdb (current=0xffff0000fa852bc0, pid 268) on processor 0 due to Breakpoint @ 0xffff8000101486cc
    [0]kdb> ss

    Entering kdb (current=0xffff0000fa852bc0, pid 268) on processor 0 due to SS trap @ 0xffff800010082ab8
    [0]kdb>

    Fixes: 44679a4f142b ("arm64: KGDB: Add step debugging support")
    Signed-off-by: Wei Li <liwei391@huawei.com>
    Tested-by: Douglas Anderson <dianders@chromium.org>
    Reviewed-by: Douglas Anderson <dianders@chromium.org>
    Link: https://lore.kernel.org/r/20200509214159.19680-2-liwei391@huawei.com
    Signed-off-by: Will Deacon <will@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/arm64/kernel/kgdb.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
    index 35f184a8fd85a..8815b5457dd0b 100644
    --- a/arch/arm64/kernel/kgdb.c
    +++ b/arch/arm64/kernel/kgdb.c
    @@ -269,7 +269,7 @@ static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr)
    if (user_mode(regs) || !kgdb_single_step)
    return DBG_HOOK_ERROR;

    - kgdb_handle_exception(1, SIGTRAP, 0, regs);
    + kgdb_handle_exception(0, SIGTRAP, 0, regs);
    return DBG_HOOK_HANDLED;
    }
    NOKPROBE_SYMBOL(kgdb_step_brk_fn);
    --
    2.25.1


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