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Date:   Sat, 24 Jul 2021 13:15:46 -0700 (PDT)
Subject:     Re: [PATCH RESEND] riscv: stacktrace: Fix NULL pointer dereference
In-Reply-To: <20210725000258.1ca59266@xhacker>
CC:     atishp@atishpatra.org, Paul Walmsley <paul.walmsley@sifive.com>,
        aou@eecs.berkeley.edu, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     jszhang3@mail.ustc.edu.cn
Message-ID: <mhng-1f8957c6-164a-46c6-b0a2-d8ae52b3cb8c@palmerdabbelt-glaptop>
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On Sat, 24 Jul 2021 09:02:58 PDT (-0700), jszhang3@mail.ustc.edu.cn wrote:
> Hi @Palmer,
>
> On Fri, 16 Jul 2021 07:07:24 -0700
> Atish Patra <atishp@atishpatra.org> wrote:
>
>> On Fri, Jul 16, 2021 at 6:47 AM Jisheng Zhang wrote:
>> >
>> > From: Jisheng Zhang <jszhang@kernel.org>
>> >
>> > When CONFIG_FRAME_POINTER=y, calling dump_stack() can always trigger
>> > NULL pointer dereference panic similar as below:
>> >
>> > [    0.396060] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.13.0-rc5+ #47
>> > [    0.396692] Hardware name: riscv-virtio,qemu (DT)
>> > [    0.397176] Call Trace:
>> > [    0.398191] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000960
>> > [    0.399487] Oops [#1]
>> > [    0.399739] Modules linked in:
>> > [    0.400135] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.13.0-rc5+ #47
>> > [    0.400570] Hardware name: riscv-virtio,qemu (DT)
>> > [    0.400926] epc : walk_stackframe+0xc4/0xdc
>> > [    0.401291]  ra : dump_backtrace+0x30/0x38
>> > [    0.401630] epc : ffffffff80004922 ra : ffffffff8000496a sp : ffffffe000f3bd00
>> > [    0.402115]  gp : ffffffff80cfdcb8 tp : ffffffe000f30000 t0 : ffffffff80d0b0cf
>> > [    0.402602]  t1 : ffffffff80d0b0c0 t2 : 0000000000000000 s0 : ffffffe000f3bd60
>> > [    0.403071]  s1 : ffffffff808bc2e8 a0 : 0000000000001000 a1 : 0000000000000000
>> > [    0.403448]  a2 : ffffffff803d7088 a3 : ffffffff808bc2e8 a4 : 6131725dbc24d400
>> > [    0.403820]  a5 : 0000000000001000 a6 : 0000000000000002 a7 : ffffffffffffffff
>> > [    0.404226]  s2 : 0000000000000000 s3 : 0000000000000000 s4 : 0000000000000000
>> > [    0.404634]  s5 : ffffffff803d7088 s6 : ffffffff808bc2e8 s7 : ffffffff80630650
>> > [    0.405085]  s8 : ffffffff80912a80 s9 : 0000000000000008 s10: ffffffff804000fc
>> > [    0.405388]  s11: 0000000000000000 t3 : 0000000000000043 t4 : ffffffffffffffff
>> > [    0.405616]  t5 : 000000000000003d t6 : ffffffe000f3baa8
>> > [    0.405793] status: 0000000000000100 badaddr: 0000000000000960 cause: 000000000000000d
>> > [    0.406135] [<ffffffff80004922>] walk_stackframe+0xc4/0xdc
>> > [    0.407032] [<ffffffff8000496a>] dump_backtrace+0x30/0x38
>> > [    0.407797] [<ffffffff803d7100>] show_stack+0x40/0x4c
>> > [    0.408234] [<ffffffff803d9e5c>] dump_stack+0x90/0xb6
>> > [    0.409019] [<ffffffff8040423e>] ptdump_init+0x20/0xc4
>> > [    0.409681] [<ffffffff800015b6>] do_one_initcall+0x4c/0x226
>> > [    0.410110] [<ffffffff80401094>] kernel_init_freeable+0x1f4/0x258
>> > [    0.410562] [<ffffffff803dba88>] kernel_init+0x22/0x148
>> > [    0.410959] [<ffffffff800029e2>] ret_from_exception+0x0/0x14
>> > [    0.412241] ---[ end trace b2ab92c901b96251 ]---
>> > [    0.413099] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
>> >
>> > The reason is the task is NULL when we finally call walk_stackframe()
>> > the NULL is passed from __dump_stack():
>> >
>> > |static void __dump_stack(void)
>> > |{
>> > |        dump_stack_print_info(KERN_DEFAULT);
>> > |        show_stack(NULL, NULL, KERN_DEFAULT);
>> > |}
>> >
>> > Fix this issue by checking "task == NULL" case in walk_stackframe().
>> >
>> > Fixes: eac2f3059e02 ("riscv: stacktrace: fix the riscv stacktrace when CONFIG_FRAME_POINTER enabled"
>
> Missed a ")" at the end here, do you want a resend?
>
> PS: This patch is missed for twice.

Sorry about that.   I remember having seen this, so I'm not sure what 
happened.  It's on fixes now, but I'm just sending up a PR so this will 
go up in the next one.

>
> Thanks
>
>> > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
>> > ---
>> >  arch/riscv/kernel/stacktrace.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
>> > index bde85fc53357..7bc8af75933a 100644
>> > --- a/arch/riscv/kernel/stacktrace.c
>> > +++ b/arch/riscv/kernel/stacktrace.c
>> > @@ -27,7 +27,7 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
>> >                 fp = frame_pointer(regs);
>> >                 sp = user_stack_pointer(regs);
>> >                 pc = instruction_pointer(regs);
>> > -       } else if (task == current) {
>> > +       } else if (task == NULL || task == current) {
>> >                 fp = (unsigned long)__builtin_frame_address(1);
>> >                 sp = (unsigned long)__builtin_frame_address(0);
>> >                 pc = (unsigned long)__builtin_return_address(0);
>> > --
>> > 2.32.0
>> >
>> >
>> >
>> > _______________________________________________
>> > linux-riscv mailing list
>> > linux-riscv@lists.infradead.org
>> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>>
>>
>> Reviewed-by: Atish Patra <atish.patra@wdc.com>
>>