From: Josh Poimboeuf <jpoim...@redhat.com> There are a handful of callers to save_stack_trace_tsk() and show_stack() which try to unwind the stack of a task other than current. In such cases, it's remotely possible that the task is running on one CPU while the unwinder is reading its stack from another CPU, causing the unwinder to see stack corruption.
These cases seem to be mostly harmless. The unwinder has checks which prevent it from following bad pointers beyond the bounds of the stack. So it's not really a bug as long as the caller understands that unwinding another task will not always succeed. In such cases, it's possible that the unwinder may read a KASAN-poisoned region of the stack. Account for that by using READ_ONCE_NOCHECK() when reading the stack of another task. Use READ_ONCE() when reading the stack of the current task, since KASAN warnings can still be useful for finding bugs in that case. Reported-by: Dmitry Vyukov <dvyu...@google.com> Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> Cc: Andy Lutomirski <l...@amacapital.net> Cc: Andy Lutomirski <l...@kernel.org> Cc: Borislav Petkov <b...@alien8.de> Cc: Brian Gerst <brge...@gmail.com> Cc: Dave Jones <da...@codemonkey.org.uk> Cc: Denys Vlasenko <dvlas...@redhat.com> Cc: H. Peter Anvin <h...@zytor.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Miroslav Benes <mbe...@suse.cz> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/4c575eb288ba9f73d498dfe0acde2f58674598f1.1483978430.git.jpoim...@redhat.com Signed-off-by: Ingo Molnar <mi...@kernel.org> (cherry picked from ms commit 84936118bdf37bda513d4a361c38181a216427e0) in the scope of https://jira.sw.ru/browse/HCI-171 and in the scope of https://jira.vzint.dev/browse/PSBM-149932 Signed-off-by: Konstantin Khorenko <khore...@virtuozzo.com> --- arch/x86/include/asm/stacktrace.h | 5 ++++- arch/x86/kernel/unwind_frame.c | 19 +++++++++++++++++-- 2 files changed, 21 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h index f8a383338352..71714402d0af 100644 --- a/arch/x86/include/asm/stacktrace.h +++ b/arch/x86/include/asm/stacktrace.h @@ -52,6 +52,8 @@ static inline bool on_stack(struct stack_info *info, void *addr, size_t len) static inline unsigned long * get_frame_pointer(struct task_struct *task, struct pt_regs *regs) { + unsigned long *frame; + if (regs) return (unsigned long *)regs->bp; @@ -59,7 +61,8 @@ get_frame_pointer(struct task_struct *task, struct pt_regs *regs) return __builtin_frame_address(0); /* bp is the last reg pushed by switch_to */ - return (unsigned long *)*(unsigned long *)task->thread.sp; + frame = (unsigned long *)task->thread.sp; + return (unsigned long *)READ_ONCE_NOCHECK(*frame); } #else static inline unsigned long * diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c index 05a9f845c417..0a7d7d265053 100644 --- a/arch/x86/kernel/unwind_frame.c +++ b/arch/x86/kernel/unwind_frame.c @@ -6,6 +6,21 @@ #define FRAME_HEADER_SIZE (sizeof(long) * 2) +/* + * This disables KASAN checking when reading a value from another task's stack, + * since the other task could be running on another CPU and could have poisoned + * the stack in the meantime. + */ +#define READ_ONCE_TASK_STACK(task, x) \ +({ \ + unsigned long val; \ + if (task == current) \ + val = READ_ONCE(x); \ + else \ + val = READ_ONCE_NOCHECK(x); \ + val; \ +}) + unsigned long unwind_get_return_address(struct unwind_state *state) { if (unwind_done(state)) @@ -44,7 +59,7 @@ static bool update_stack_state(struct unwind_state *state, /* Move state to the next frame: */ state->bp = next_bp; addr_p = state->bp + 1; - addr = READ_ONCE(*addr_p); + addr = READ_ONCE_TASK_STACK(state->task, *addr_p); state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx, addr, addr_p); @@ -113,7 +128,7 @@ bool unwind_next_frame(struct unwind_state *state) if (unwind_end(state)) goto the_end; - next_bp = (unsigned long *)READ_ONCE(*state->bp); + next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task,*state->bp); /* make sure the next frame's data is accessible */ if (!update_stack_state(state, next_bp)) { -- 2.24.3 _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel
