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Fri, 28 Jul 2023 14:57:20 +0800 From: Enze Li To: Jinyang He Cc: chenhuacai@kernel.org, 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, yangtiezhu@loongson.cn, dvyukov@google.com Subject: Re: [PATCH 2/4 v2] LoongArch: Get stack without NMI when providing regs parameter In-Reply-To: (Jinyang He's message of "Wed, 26 Jul 2023 10:59:06 +0800") References: <20230725061451.1231480-1-lienze@kylinos.cn> <20230725061451.1231480-3-lienze@kylinos.cn> Date: Fri, 28 Jul 2023 14:57:11 +0800 Message-ID: <87o7jwa5h4.fsf@kylinos.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1EABBA0003 X-Stat-Signature: g6s39xhpm67ioxa64ddojscbmj9oyyk4 X-Rspam-User: X-HE-Tag: 1690527449-879015 X-HE-Meta: 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 zD69Z5JT OqLC8seitI9MpUWkEsEnqFFFFQKMWOgvwjjqWt1TOjTpNUnU= 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: 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 ] =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 | 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 =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_address(0); >> + if (regs) >> + memcpy(&dummyregs, regs, sizeof(*regs)); >> + else { >> + dummyregs.regs[3] =3D (unsigned long)__builtin_frame_address(0); >> + dummyregs.csr_era =3D (unsigned long)__builtin_return_address(0); >> + } >> } else { >> - regs->regs[3] =3D thread_saved_fp(task); >> - regs->csr_era =3D thread_saved_ra(task); >> + if (regs) >> + memcpy(&dummyregs, regs, sizeof(*regs)); >> + else { >> + dummyregs.regs[3] =3D thread_saved_fp(task); >> + dummyregs.csr_era =3D thread_saved_ra(task); >> + } >> } >> + regs =3D &dummyregs; >> + Hi Jinyang, > > if (!regs) { > =C2=A0=C2=A0=C2=A0 regs =3D &dummyregs; > > =C2=A0=C2=A0=C2=A0 if (task =3D=3D current) { > =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 regs->regs[3] =3D (unsigned long)__= builtin_frame_address(0); > =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 regs->csr_era =3D (unsigned long)__= builtin_return_address(0); > =C2=A0=C2=A0=C2=A0 } else { > =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 regs->regs[3] =3D thread_saved_fp(t= ask); > =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 regs->csr_era =3D thread_saved_ra(t= ask); > =C2=A0=C2=A0=C2=A0 } > =C2=A0=C2=A0=C2=A0 regs->regs[1] =3D 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] =3D 0; >> for (unwind_start(&state, task, regs); >> !unwind_done(&state) && !unwind_error(&state); unwind_next_frame= (&state)) {