[PATCH] riscv: fix out of bounds in walk_stackframe

[Alexandre Ghiti]

Oh and BTW, any idea why linux-riscv was not in CC for the initial report?

On 28/09/2023 10:02, Alexandre Ghiti wrote:
> Hi Edward,
>
> On 26/09/2023 13:43, Edward AD wrote:
>> Increase the check on the frame after assigning its value. This is to 
>> prevent
>> frame access from crossing boundaries.
>>
>> Closes: 
>> https://lore.kernel.org/all/20230926105949.1025995-2-twuufnxlz@gmail.com/
>> Fixes: 5d8544e2d007 ("RISC-V: Generic library routines and assembly")
>> Reported-and-tested-by: 
>> syzbot+8d2757d62d403b2d9275 at syzkaller.appspotmail.com
>> Link: 
>> https://lore.kernel.org/all/0000000000000170df0605ccf91a@google.com/T/
>> Signed-off-by: Edward AD <twuufnxlz at gmail.com>
>> ---
>>   arch/riscv/kernel/stacktrace.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/riscv/kernel/stacktrace.c 
>> b/arch/riscv/kernel/stacktrace.c
>> index 64a9c093aef9..53bd18672329 100644
>> --- a/arch/riscv/kernel/stacktrace.c
>> +++ b/arch/riscv/kernel/stacktrace.c
>> @@ -54,6 +54,8 @@ void notrace walk_stackframe(struct task_struct 
>> *task, struct pt_regs *regs,
>>               break;
>>           /* Unwind stack frame */
>>           frame = (struct stackframe *)fp - 1;
>> +        if (!virt_addr_valid(frame))
>> +            break;
>>           sp = fp;
>>           if (regs && (regs->epc == pc) && (frame->fp & 0x7)) {
>>               fp = frame->ra;
>
>
> virt_addr_valid() works on kernel linear addresses, not on vmalloc 
> addresses, which is the case here  (0xff20000006d37c38 belongs to the 
> vmalloc region: see 
> https://elixir.bootlin.com/linux/latest/source/Documentation/riscv/vm-layout.rst#L125). 
> So this fix can't work.
>
> I'm a bit surprised though of this out-of-bounds access since 
> CONFIG_FRAME_POINTER is enabled, so there may be a real issue here 
> (the console output is horrible, lots of backtraces, which is weird), 
> so it may be worth digging into that.
>
> Thanks,
>
> Alex
>
>
>
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