On Wed, Jul 26 2023 at 10:59:06 AM +0800, Jinyang He wrote:
> On 2023-07-25 14:14, Enze Li wrote:
>
>> Currently, arch_stack_walk() can only get the full stack information
>> including NMI. This is because the implementation of arch_stack_walk()
>> is forced to ignore the information passed by the regs parameter and use
>> the current stack information instead.
>>
>> For some detection systems like KFENCE, only partial stack information
>> is needed. In particular, the stack frame where the interrupt occurred.
>>
>> To support KFENCE, this patch modifies the implementation of the
>> arch_stack_walk() function so that if this function is called with the
>> regs argument passed, it retains all the stack information in regs and
>> uses it to provide accurate information.
>>
>> Before the patch applied, I get,
>> [ 1.531195 ] ==================================================================
>> [ 1.531442 ] BUG: KFENCE: out-of-bounds read in stack_trace_save_regs+0x48/0x6c
>> [ 1.531442 ]
>> [ 1.531900 ] Out-of-bounds read at 0xffff800012267fff (1B left of kfence-#12):
>> [ 1.532046 ] stack_trace_save_regs+0x48/0x6c
>> [ 1.532169 ] kfence_report_error+0xa4/0x528
>> [ 1.532276 ] kfence_handle_page_fault+0x124/0x270
>> [ 1.532388 ] no_context+0x50/0x94
>> [ 1.532453 ] do_page_fault+0x1a8/0x36c
>> [ 1.532524 ] tlb_do_page_fault_0+0x118/0x1b4
>> [ 1.532623 ] test_out_of_bounds_read+0xa0/0x1d8
>> [ 1.532745 ] kunit_generic_run_threadfn_adapter+0x1c/0x28
>> [ 1.532854 ] kthread+0x124/0x130
>> [ 1.532922 ] ret_from_kernel_thread+0xc/0xa4
>> <snip>
>>
>> With this patch applied, I get the correct stack information.
>> [ 1.320220 ] ==================================================================
>> [ 1.320401 ] BUG: KFENCE: out-of-bounds read in test_out_of_bounds_read+0xa8/0x1d8
>> [ 1.320401 ]
>> [ 1.320898 ] Out-of-bounds read at 0xffff800012257fff (1B left of kfence-#10):
>> [ 1.321134 ] test_out_of_bounds_read+0xa8/0x1d8
>> [ 1.321264 ] kunit_generic_run_threadfn_adapter+0x1c/0x28
>> [ 1.321392 ] kthread+0x124/0x130
>> [ 1.321459 ] ret_from_kernel_thread+0xc/0xa4
>> <snip>
>>
>> Signed-off-by: Enze Li <lienze@xxxxxxxxxx>
>> ---
>> arch/loongarch/kernel/stacktrace.c | 20 ++++++++++++++------
>> 1 file changed, 14 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/loongarch/kernel/stacktrace.c b/arch/loongarch/kernel/stacktrace.c
>> index 2463d2fea21f..9dab30ae68ec 100644
>> --- a/arch/loongarch/kernel/stacktrace.c
>> +++ b/arch/loongarch/kernel/stacktrace.c
>> @@ -18,16 +18,24 @@ void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
>> struct pt_regs dummyregs;
>> struct unwind_state state;
>> - regs = &dummyregs;
>> -
>> if (task == current) {
>> - regs->regs[3] = (unsigned long)__builtin_frame_address(0);
>> - regs->csr_era = (unsigned long)__builtin_return_address(0);
>> + if (regs)
>> + memcpy(&dummyregs, regs, sizeof(*regs));
>> + else {
>> + dummyregs.regs[3] = (unsigned long)__builtin_frame_address(0);
>> + dummyregs.csr_era = (unsigned long)__builtin_return_address(0);
>> + }
>> } else {
>> - regs->regs[3] = thread_saved_fp(task);
>> - regs->csr_era = thread_saved_ra(task);
>> + if (regs)
>> + memcpy(&dummyregs, regs, sizeof(*regs));
>> + else {
>> + dummyregs.regs[3] = thread_saved_fp(task);
>> + dummyregs.csr_era = thread_saved_ra(task);
>> + }
>> }
>> + regs = &dummyregs;
>> +
Hi Jinyang,
>
> if (!regs) {
> regs = &dummyregs;
>
> if (task == current) {
> regs->regs[3] = (unsigned long)__builtin_frame_address(0);
> regs->csr_era = (unsigned long)__builtin_return_address(0);
> } else {
> regs->regs[3] = thread_saved_fp(task);
> regs->csr_era = thread_saved_ra(task);
> }
> regs->regs[1] = 0;
> }
Excellent! FWIW, it looks easy to understand.
I've tested this patch, and it works well. Thank you.
Cheers!
Enze
>
> BTW, I remembered that __unwind_start() deals with this issue in regs,
> task and current. arch_stack_walk() is unnecessary to provide current
> or task regs if we fix the unwind_start() skip its parent frame
> (caller is arch_stack_walk). But the current state is better, I think.
>
>
> Thanks,
>
> Jinyang
>
>> regs->regs[1] = 0;
>> for (unwind_start(&state, task, regs);
>> !unwind_done(&state) && !unwind_error(&state); unwind_next_frame(&state)) {
