From: Ingo Molnar Date: Fri, 17 Nov 2006 04:57:49 +0000 (+0100) Subject: [PATCH] x86_64: stack unwinder crash fix X-Git-Tag: v2.6.19~78 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0796bdb7e9e4a48b401f4fba1ee5dc79a45528ef;p=linux-2.6 [PATCH] x86_64: stack unwinder crash fix the new dwarf2 unwinder crashes while trying to dump the stack: Leftover inexact backtrace: Unable to handle kernel paging request at ffffffff82800000 RIP: [] dump_trace+0x35b/0x3d2 PGD 203027 PUD 205027 PMD 0 Oops: 0000 [2] PREEMPT SMP CPU 0 Modules linked in: Pid: 30, comm: khelper Not tainted 2.6.19-rc6-rt1 #11 RIP: 0010:[] [] dump_trace+0x35b/0x3d2 RSP: 0000:ffff81003fb9d848 EFLAGS: 00010006 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffffffff805b3520 RDI: 0000000000000000 RBP: ffffffff827ffff9 R08: ffffffff80aad000 R09: 0000000000000005 R10: ffffffff80aae000 R11: ffffffff8037961b R12: ffff81003fb9d858 R13: 0000000000000000 R14: ffffffff80598460 R15: ffffffff80ab1fc0 FS: 0000000000000000(0000) GS:ffffffff806c4200(0000) knlGS:0000000000000000 CS: 0010 DS: 0018 ES: 0018 CR0: 000000008005003b CR2: ffffffff82800000 CR3: 0000000000201000 CR4: 00000000000006e0 this crash happened because it did not sanitize the dwarf2 data it got, and got an unaligned stack pointer - which happily walked past the process stack (and eventually reached the end of kernel memory and pagefaulted there) due to this naive iteration condition: HANDLE_STACK (((long) stack & (THREAD_SIZE-1)) != 0); note that i386 is alot more conservative when it comes to trusting stack pointers: static inline int valid_stack_ptr(struct thread_info *tinfo, void *p) { return p > (void *)tinfo && p < (void *)tinfo + THREAD_SIZE - 3; } but the x86_64 code did not take this bit of i386 code. The fix is to align the stack pointer. Signed-off-by: Ingo Molnar Cc: Andi Kleen Cc: Jan Beulich Cc: Thomas Gleixner Cc: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c index 7819022a8d..a153d0a01b 100644 --- a/arch/x86_64/kernel/traps.c +++ b/arch/x86_64/kernel/traps.c @@ -290,6 +290,12 @@ void dump_trace(struct task_struct *tsk, struct pt_regs *regs, unsigned long * s if (tsk && tsk != current) stack = (unsigned long *)tsk->thread.rsp; } + /* + * Align the stack pointer on word boundary, later loops + * rely on that (and corruption / debug info bugs can cause + * unaligned values here): + */ + stack = (unsigned long *)((unsigned long)stack & ~(sizeof(long)-1)); /* * Print function call entries within a stack. 'cond' is the