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[118.7.246.222]) by smtp.gmail.com with ESMTPSA id x7sm12857733pfa.125.2019.07.01.22.31.59 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 01 Jul 2019 22:32:01 -0700 (PDT) From: Eiichi Tsukata To: rostedt@goodmis.org, edwintorok@gmail.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org Cc: Eiichi Tsukata Subject: [PATCH] x86/stacktrace: Do not access user space memory unnecessarily Date: Tue, 2 Jul 2019 14:31:51 +0900 Message-Id: <20190702053151.26922-1-devel@etsukata.com> X-Mailer: git-send-email 2.21.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Put the boundary check before it accesses user space to prevent unnecessary access which might crash the machine. Especially, ftrace preemptirq/irq_disable event with user stack trace option can trigger SEGV in pid 1 which leads to panic. Reproducer: CONFIG_PREEMPTIRQ_TRACEPOINTS=y # echo 1 > events/preemptirq/enable # echo userstacktrace > trace_options Output: Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b CPU: 1 PID: 1 Comm: systemd Not tainted 5.2.0-rc7+ #10 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) Call Trace: dump_stack+0x67/0x90 panic+0x100/0x2c6 do_exit.cold+0x4e/0x101 do_group_exit+0x3a/0xa0 get_signal+0x14a/0x8e0 do_signal+0x36/0x650 exit_to_usermode_loop+0x92/0xb0 prepare_exit_to_usermode+0x6f/0xb0 retint_user+0x8/0x18 RIP: 0033:0x55be7ad1c89f Code: Bad RIP value. RSP: 002b:00007ffe329a4b00 EFLAGS: 00010202 RAX: 0000000000000768 RBX: 00007ffe329a4ba0 RCX: 00007ff0063aa469 RDX: 00007ff0066761de RSI: 00007ffe329a4b20 RDI: 0000000000000768 RBP: 000000000000000b R08: 0000000000000000 R09: 00007ffe329a4e2f R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000768 R13: 0000000000000000 R14: 0000000000000004 R15: 000055be7b3d3560 Kernel Offset: 0x2a000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff) Fixes: 02b67518e2b1 ("tracing: add support for userspace stacktraces in tracing/iter_ctrl") Signed-off-by: Eiichi Tsukata --- arch/x86/kernel/stacktrace.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c index 2abf27d7df6b..6d0c608ffe34 100644 --- a/arch/x86/kernel/stacktrace.c +++ b/arch/x86/kernel/stacktrace.c @@ -123,12 +123,12 @@ void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie, while (1) { struct stack_frame_user frame; + if ((unsigned long)fp < regs->sp) + break; frame.next_fp = NULL; frame.ret_addr = 0; if (!copy_stack_frame(fp, &frame)) break; - if ((unsigned long)fp < regs->sp) - break; if (frame.ret_addr) { if (!consume_entry(cookie, frame.ret_addr, false)) return; -- 2.21.0