On Fri, Jul 21, 2023 at 9:50 AM Enze Li <lienze@xxxxxxxxxx> wrote:
>
> Hi Huacai,
>
> Thanks for your review.
>
> On Wed, Jul 19 2023 at 11:17:14 PM +0800, Huacai Chen wrote:
>
> > Hi, Enze,
> >
> > On Wed, Jul 19, 2023 at 4:34 PM Enze Li <lienze@xxxxxxxxxx> wrote:
> >>
> >> Currently, executing 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 | 16 ++++++++++------
> >> 1 file changed, 10 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/arch/loongarch/kernel/stacktrace.c b/arch/loongarch/kernel/stacktrace.c
> >> index 2463d2fea21f..21f60811e26f 100644
> >> --- a/arch/loongarch/kernel/stacktrace.c
> >> +++ b/arch/loongarch/kernel/stacktrace.c
> >> @@ -18,16 +18,20 @@ 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 {
> > When "task != current", we don't need to handle the "regs != NULL" case?
> >
> > Huacai
> >
>
> So far, I have not encountered this situation. I'm not sure what
> problems would arise from extending the modifications with "task !=
> current".
>
> However, these modifications now are sufficient for the KFENCE
> system. I would suggest that we don't modify other parts until we
> encounter problems. This way, we can forge ahead steadily.
I don't think so. In my opinion, "partial stack information" is a
clear requirement, whether the task is current or not.
So, if the input regs is not NULL, we should always
memcpy(&dummyregs, regs, sizeof(*regs));
Or we may listen to Tiezhu's idea?
Huacai
>
> Best Regards,
> Enze
>
> >> - regs->regs[3] = thread_saved_fp(task);
> >> - regs->csr_era = thread_saved_ra(task);
> >> + dummyregs.regs[3] = thread_saved_fp(task);
> >> + dummyregs.csr_era = thread_saved_ra(task);
> >> }
> >>
> >> + regs = &dummyregs;
> >> +
> >> regs->regs[1] = 0;
> >> for (unwind_start(&state, task, regs);
> >> !unwind_done(&state) && !unwind_error(&state); unwind_next_frame(&state)) {
> >> --
> >> 2.34.1
> >>
> >>
