linux-kernel - [PATCH -next v2] x86: Prevent KASAN false positive warnings in __show

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Message-Id: <20250829094744.3133324-1-wutengda@huaweicloud.com>
Date: Fri, 29 Aug 2025 09:47:44 +0000
From: Tengda Wu <wutengda@...weicloud.com>
To: x86@...nel.org,
	jpoimboe@...nel.org,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org,
	Tengda Wu <wutengda@...weicloud.com>
Subject: [PATCH -next v2] x86: Prevent KASAN false positive warnings in __show_regs

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 `regs->` contents,
resulting in false positive reports. [1][2]

The specific issue occurs as follows:

Task A (walk other task's stack)            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 data 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

Fix this by detecting asynchronous stack unwinding scenarios through
checking whether the `regs` are located in the current task's stack
during unwinding, and disabling KASAN checks when this scenario occurs.

[1] https://lore.kernel.org/all/000000000000cb8e3a05c4ed84bb@google.com/
[2] KASAN out-of-bounds:
[332706.552324] BUG: KASAN: out-of-bounds in __show_regs+0x4b/0x340
[332706.552433] Read of size 8 at addr ffff88d24999fb20 by task sysrq_t_test.sh/3977032
[332706.552562]
[332706.552652] CPU: 36 PID: 3977032 Comm: sysrq_t_test.sh Kdump: loaded Not tainted 6.6.0+ #20
[332706.552783] Hardware name: Huawei RH2288H V3/BC11HGSA0, BIOS 3.35 10/20/2016
[332706.552906] Call Trace:
[332706.552998]  <TASK>
[332706.553089]  dump_stack_lvl+0x32/0x50
[332706.553193]  print_address_description.constprop.0+0x6b/0x3d0
[332706.553303]  print_report+0xbe/0x280
[332706.553409]  ? __virt_addr_valid+0xed/0x160
[332706.553512]  ? __show_regs+0x4b/0x340
[332706.553612]  kasan_report+0xa8/0xe0
[332706.553716]  ? __show_regs+0x4b/0x340
[332706.553816]  ? asm_exc_page_fault+0x22/0x30
[332706.553919]  __show_regs+0x4b/0x340
[332706.554021]  ? asm_exc_page_fault+0x22/0x30
[332706.554123]  show_trace_log_lvl+0x274/0x3b0
[332706.554229]  ? load_elf_binary+0xf6e/0x1610
[332706.554330]  ? rep_stos_alternative+0x40/0x80
[332706.554439]  sched_show_task+0x211/0x290
[332706.554544]  ? __pfx_sched_show_task+0x10/0x10
[332706.554648]  ? _find_next_bit+0x6/0xc0
[332706.554749]  ? _find_next_bit+0x37/0xc0
[332706.554852]  show_state_filter+0x72/0x130
[332706.554956]  sysrq_handle_showstate+0x7/0x10
[332706.555062]  __handle_sysrq+0x146/0x2d0
[332706.555165]  write_sysrq_trigger+0x2f/0x50
[332706.555270]  proc_reg_write+0xdd/0x140
[332706.555372]  vfs_write+0x1ff/0x5f0
[332706.555474]  ? __pfx_vfs_write+0x10/0x10
[332706.555576]  ? __pfx___handle_mm_fault+0x10/0x10
[332706.555682]  ? __fget_light+0x99/0xf0
[332706.555785]  ksys_write+0xb8/0x150
[332706.555887]  ? __pfx_ksys_write+0x10/0x10
[332706.555989]  ? ktime_get_coarse_real_ts64+0x4e/0x70
[332706.556094]  do_syscall_64+0x55/0x100
[332706.556196]  entry_SYSCALL_64_after_hwframe+0x78/0xe2

Fixes: 3b3fa11bc700 ("x86/dumpstack: Print any pt_regs found on the stack")
Signed-off-by: Tengda Wu <wutengda@...weicloud.com>
---
v2: Use kasan_disable_current() instead of __no_sanitize_address.
v1: https://lore.kernel.org/all/20250818130715.2904264-1-wutengda@huaweicloud.com/

 arch/x86/kernel/dumpstack.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 71ee20102a8a..5413534de490 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -152,6 +152,18 @@ void show_iret_regs(struct pt_regs *regs, const char *log_lvl)
 static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs,
 				  bool partial, const char *log_lvl)
 {
+	bool kasan_disabled = false;
+
+	/*
+	 * When 'regs' resides in another task's stack space, KASAN should be
+	 * disabled to prevent false positives during 'regs->' operation, as
+	 * the 'regs' contents may change concurrently with task execution.
+	 */
+	if (!object_is_on_stack(regs)) {
+		kasan_disable_current();
+		kasan_disabled = true;
+	}
+
 	/*
 	 * These on_stack() checks aren't strictly necessary: the unwind code
 	 * has already validated the 'regs' pointer.  The checks are done for
@@ -173,6 +185,9 @@ static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs,
 		 */
 		show_iret_regs(regs, log_lvl);
 	}
+
+	if (kasan_disabled)
+		kasan_enable_current();
 }
 
 /*
-- 
2.34.1