5.4-stable review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
[ Upstream commit 2c118f50d7fd4d9aefc4533a26f83338b2906b7a ]
Commit:
2e4be0d011f2 ("x86/show_trace_log_lvl: Ensure stack pointer is aligned, again")
was intended to ensure alignment of the stack pointer; but it also moved the initialization of the "stack" variable down into the loop header.
This was likely intended as a no-op cleanup, since the commit message does not mention it; however, this caused a behavioral change because the value of "regs" is different between the two places.
Originally, get_stack_pointer() used the regs provided by the caller; after that commit, get_stack_pointer() instead uses the regs at the top of the stack frame the unwinder is looking at. Often, there are no such regs at all, and "regs" is NULL, causing get_stack_pointer() to fall back to the task's current stack pointer, which is not what we want here, but probably happens to mostly work. Other times, the original regs will point to another regs frame - in that case, the linear guess unwind logic in show_trace_log_lvl() will start unwinding too far up the stack, causing the first frame found by the proper unwinder to never be visited, resulting in a stack trace consisting purely of guess lines.
Fix it by moving the "stack = " assignment back where it belongs.
Fixes: 2e4be0d011f2 ("x86/show_trace_log_lvl: Ensure stack pointer is aligned, again") Signed-off-by: Jann Horn jannh@google.com Signed-off-by: Ingo Molnar mingo@kernel.org Link: https://lore.kernel.org/r/20250325-2025-03-unwind-fixes-v1-2-acd774364768@go... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/dumpstack.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index 9b2bbb66d0c87..caf14c49539ba 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -171,6 +171,7 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs, printk("%sCall Trace:\n", log_lvl);
unwind_start(&state, task, regs, stack); + stack = stack ?: get_stack_pointer(task, regs); regs = unwind_get_entry_regs(&state, &partial);
/* @@ -189,9 +190,7 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs, * - hardirq stack * - entry stack */ - for (stack = stack ?: get_stack_pointer(task, regs); - stack; - stack = stack_info.next_sp) { + for (; stack; stack = stack_info.next_sp) { const char *stack_name;
stack = PTR_ALIGN(stack, sizeof(long));