6.6-stable review patch. If anyone has any objections, please let me know.
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From: Tengda Wu wutengda@huaweicloud.com
[ Upstream commit ced37e9ceae50e4cb6cd058963bd315ec9afa651 ]
When triggering a stack dump via sysrq (echo t > /proc/sysrq-trigger), KASAN may report false-positive out-of-bounds access:
BUG: KASAN: out-of-bounds in __show_regs+0x4b/0x340 Call Trace: dump_stack_lvl print_address_description.constprop.0 print_report __show_regs show_trace_log_lvl sched_show_task show_state_filter sysrq_handle_showstate __handle_sysrq write_sysrq_trigger proc_reg_write vfs_write ksys_write do_syscall_64 entry_SYSCALL_64_after_hwframe
The issue occurs as follows:
Task A (walk other tasks' stacks) Task B (running) 1. echo t > /proc/sysrq-trigger show_trace_log_lvl regs = unwind_get_entry_regs() show_regs_if_on_stack(regs) 2. The stack value pointed by `regs` keeps changing, and so are the tags in its KASAN shadow region. __show_regs(regs) regs->ax, regs->bx, ... 3. hit KASAN redzones, OOB
When task A walks task B's stack without suspending it, the continuous changes in task B's stack (and corresponding KASAN shadow tags) may cause task A to hit KASAN redzones when accessing obsolete values on the stack, resulting in false positive reports.
Simply stopping the task before unwinding is not a viable fix, as it would alter the state intended to inspect. This is especially true for diagnosing misbehaving tasks (e.g., in a hard lockup), where stopping might fail or hide the root cause by changing the call stack.
Therefore, fix this by disabling KASAN checks during asynchronous stack unwinding, which is identified when the unwinding task does not match the current task (task != current).
[ bp: Align arguments on function's opening brace. ]
Fixes: 3b3fa11bc700 ("x86/dumpstack: Print any pt_regs found on the stack") Signed-off-by: Tengda Wu wutengda@huaweicloud.com Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Reviewed-by: Andrey Ryabinin ryabinin.a.a@gmail.com Acked-by: Josh Poimboeuf jpoimboe@kernel.org Link: https://patch.msgid.link/all/20251023090632.269121-1-wutengda@huaweicloud.co... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/dumpstack.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index 52dc5839d1e8e..0667d947d82bb 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -183,8 +183,8 @@ static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs, * in false positive reports. Disable instrumentation to avoid those. */ __no_kmsan_checks -static void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs, - unsigned long *stack, const char *log_lvl) +static void __show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs, + unsigned long *stack, const char *log_lvl) { struct unwind_state state; struct stack_info stack_info = {0}; @@ -305,6 +305,25 @@ static void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs, } }
+static void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs, + unsigned long *stack, const char *log_lvl) +{ + /* + * Disable KASAN to avoid false positives during walking another + * task's stacks, as values on these stacks may change concurrently + * with task execution. + */ + bool disable_kasan = task && task != current; + + if (disable_kasan) + kasan_disable_current(); + + __show_trace_log_lvl(task, regs, stack, log_lvl); + + if (disable_kasan) + kasan_enable_current(); +} + void show_stack(struct task_struct *task, unsigned long *sp, const char *loglvl) {