2.6.32-longterm review patch. If anyone has any objections, please let me know.
------------------ commit eddd3826a1a0190e5235703d1e666affa4d13b96 upstream. Dmitry Vyukov reported the following using trinity and the memory error detector AddressSanitizer (https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel). [ 124.575597] ERROR: AddressSanitizer: heap-buffer-overflow on address ffff88002e280000 [ 124.576801] ffff88002e280000 is located 131938492886538 bytes to the left of 28857600-byte region [ffffffff81282e0a, ffffffff82e0830a) [ 124.578633] Accessed by thread T10915: [ 124.579295] inlined in describe_heap_address ./arch/x86/mm/asan/report.c:164 [ 124.579295] #0 ffffffff810dd277 in asan_report_error ./arch/x86/mm/asan/report.c:278 [ 124.580137] #1 ffffffff810dc6a0 in asan_check_region ./arch/x86/mm/asan/asan.c:37 [ 124.581050] #2 ffffffff810dd423 in __tsan_read8 ??:0 [ 124.581893] #3 ffffffff8107c093 in get_wchan ./arch/x86/kernel/process_64.c:444 The address checks in the 64bit implementation of get_wchan() are wrong in several ways: - The lower bound of the stack is not the start of the stack page. It's the start of the stack page plus sizeof (struct thread_info) - The upper bound must be: top_of_stack - TOP_OF_KERNEL_STACK_PADDING - 2 * sizeof(unsigned long). The 2 * sizeof(unsigned long) is required because the stack pointer points at the frame pointer. The layout on the stack is: ... IP FP ... IP FP. So we need to make sure that both IP and FP are in the bounds. Fix the bound checks and get rid of the mix of numeric constants, u64 and unsigned long. Making all unsigned long allows us to use the same function for 32bit as well. Use READ_ONCE() when accessing the stack. This does not prevent a concurrent wakeup of the task and the stack changing, but at least it avoids TOCTOU. Also check task state at the end of the loop. Again that does not prevent concurrent changes, but it avoids walking for nothing. Add proper comments while at it. Reported-by: Dmitry Vyukov <dvyu...@google.com> Reported-by: Sasha Levin <sasha.le...@oracle.com> Based-on-patch-from: Wolfram Gloger <wm...@dent.med.uni-muenchen.de> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Reviewed-by: Borislav Petkov <b...@alien8.de> Reviewed-by: Dmitry Vyukov <dvyu...@google.com> Cc: Andrey Ryabinin <ryabinin....@gmail.com> Cc: Andy Lutomirski <l...@amacapital.net> Cc: Andrey Konovalov <andreyk...@google.com> Cc: Kostya Serebryany <k...@google.com> Cc: Alexander Potapenko <gli...@google.com> Cc: kasan-dev <kasan-...@googlegroups.com> Cc: Denys Vlasenko <dvlas...@redhat.com> Cc: Andi Kleen <a...@linux.intel.com> Cc: Wolfram Gloger <wm...@dent.med.uni-muenchen.de> Link: http://lkml.kernel.org/r/20150930083302.694788...@linutronix.de Signed-off-by: Thomas Gleixner <t...@linutronix.de> [bwh: Backported to 3.2: - s/READ_ONCE/ACCESS_ONCE/ - Remove use of TOP_OF_KERNEL_STACK_PADDING, not defined here and would be defined as 0] Signed-off-by: Ben Hutchings <b...@decadent.org.uk> (cherry picked from commit 5311d93d0d33ae878d5fbb35ea5693b9c813ba04) Signed-off-by: Willy Tarreau <w...@1wt.eu> --- arch/x86/kernel/process_64.c | 52 +++++++++++++++++++++++++++++++++++--------- 1 file changed, 42 insertions(+), 10 deletions(-) diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 39493bc..936b0ba 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -550,27 +550,59 @@ void set_personality_ia32(void) current_thread_info()->status |= TS_COMPAT; } +/* + * Called from fs/proc with a reference on @p to find the function + * which called into schedule(). This needs to be done carefully + * because the task might wake up and we might look at a stack + * changing under us. + */ unsigned long get_wchan(struct task_struct *p) { - unsigned long stack; - u64 fp, ip; + unsigned long start, bottom, top, sp, fp, ip; int count = 0; if (!p || p == current || p->state == TASK_RUNNING) return 0; - stack = (unsigned long)task_stack_page(p); - if (p->thread.sp < stack || p->thread.sp >= stack+THREAD_SIZE) + + start = (unsigned long)task_stack_page(p); + if (!start) + return 0; + + /* + * Layout of the stack page: + * + * ----------- topmax = start + THREAD_SIZE - sizeof(unsigned long) + * PADDING + * ----------- top = topmax - TOP_OF_KERNEL_STACK_PADDING + * stack + * ----------- bottom = start + sizeof(thread_info) + * thread_info + * ----------- start + * + * The tasks stack pointer points at the location where the + * framepointer is stored. The data on the stack is: + * ... IP FP ... IP FP + * + * We need to read FP and IP, so we need to adjust the upper + * bound by another unsigned long. + */ + top = start + THREAD_SIZE; + top -= 2 * sizeof(unsigned long); + bottom = start + sizeof(struct thread_info); + + sp = ACCESS_ONCE(p->thread.sp); + if (sp < bottom || sp > top) return 0; - fp = *(u64 *)(p->thread.sp); + + fp = ACCESS_ONCE(*(unsigned long *)sp); do { - if (fp < (unsigned long)stack || - fp >= (unsigned long)stack+THREAD_SIZE) + if (fp < bottom || fp > top) return 0; - ip = *(u64 *)(fp+8); + ip = ACCESS_ONCE(*(unsigned long *)(fp + sizeof(unsigned long))); if (!in_sched_functions(ip)) return ip; - fp = *(u64 *)fp; - } while (count++ < 16); + fp = ACCESS_ONCE(*(unsigned long *)fp); + } while (count++ < 16 && p->state != TASK_RUNNING); return 0; } -- 1.7.12.2.21.g234cd45.dirty -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
