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Fri, 21 Jul 2023 09:49:29 +0800 From: Enze Li To: Huacai Chen Cc: kernel@xen0n.name, loongarch@lists.linux.dev, glider@google.com, elver@google.com, akpm@linux-foundation.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, zhangqing@loongson.cn, yangtiezhu@loongson.cn, dvyukov@google.com Subject: Re: [PATCH 2/4] LoongArch: Get stack without NMI when providing regs parameter In-Reply-To: (Huacai Chen's message of "Wed, 19 Jul 2023 23:17:14 +0800") References: <20230719082732.2189747-1-lienze@kylinos.cn> <20230719082732.2189747-3-lienze@kylinos.cn> Date: Fri, 21 Jul 2023 09:49:20 +0800 Message-ID: <87tttyf2zj.fsf@kylinos.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 59653C0007 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: o4rtext366kwe93m7fazbojyptm1aq9p X-HE-Tag: 1689904175-893625 X-HE-Meta: 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 DPdqQmdr jRHAdTwhPHzdmMM0Za1tcHk478LlCwmq+hFd0Mxm5GqclieE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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=E2=80=AFPM Enze Li 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 ] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >> [ 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 kfe= nce-#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 >> >> >> With this patch applied, I get the correct stack information. >> [ 1.320220 ] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >> [ 1.320401 ] BUG: KFENCE: out-of-bounds read in test_out_of_bounds_re= ad+0xa8/0x1d8 >> [ 1.320401 ] >> [ 1.320898 ] Out-of-bounds read at 0xffff800012257fff (1B left of kfe= nce-#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 >> >> >> Signed-off-by: Enze Li >> --- >> 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 =3D &dummyregs; >> - >> if (task =3D=3D current) { >> - regs->regs[3] =3D (unsigned long)__builtin_frame_address= (0); >> - regs->csr_era =3D (unsigned long)__builtin_return_addres= s(0); >> + if (regs) >> + memcpy(&dummyregs, regs, sizeof(*regs)); >> + else { >> + dummyregs.regs[3] =3D (unsigned long)__builtin_f= rame_address(0); >> + dummyregs.csr_era =3D (unsigned long)__builtin_r= eturn_address(0); >> + } >> } else { > When "task !=3D current", we don't need to handle the "regs !=3D NULL" ca= se? > > Huacai > So far, I have not encountered this situation. I'm not sure what problems would arise from extending the modifications with "task !=3D 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. Best Regards, Enze >> - regs->regs[3] =3D thread_saved_fp(task); >> - regs->csr_era =3D thread_saved_ra(task); >> + dummyregs.regs[3] =3D thread_saved_fp(task); >> + dummyregs.csr_era =3D thread_saved_ra(task); >> } >> >> + regs =3D &dummyregs; >> + >> regs->regs[1] =3D 0; >> for (unwind_start(&state, task, regs); >> !unwind_done(&state) && !unwind_error(&state); unwind_next_= frame(&state)) { >> -- >> 2.34.1 >> >>