[tip: objtool/urgent] x86/show_trace_log_lvl: Ensure stack pointer is aligned, again

[tip-bot2 for Vernon Lovejoy]

The following commit has been merged into the objtool/urgent branch of tip:

Commit-ID:     2e4be0d011f21593c6b316806779ba1eba2cd7e0
Gitweb:        https://git.kernel.org/tip/2e4be0d011f21593c6b316806779ba1eba2cd7e0
Author:        Vernon Lovejoy <vlovejoy@xxxxxxxxxx>
AuthorDate:    Fri, 12 May 2023 12:42:32 +02:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Tue, 16 May 2023 06:31:04 -07:00

x86/show_trace_log_lvl: Ensure stack pointer is aligned, again

The commit e335bb51cc15 ("x86/unwind: Ensure stack pointer is aligned")
tried to align the stack pointer in show_trace_log_lvl(), otherwise the
"stack < stack_info.end" check can't guarantee that the last read does
not go past the end of the stack.

However, we have the same problem with the initial value of the stack
pointer, it can also be unaligned. So without this patch this trivial
kernel module

	#include <linux/module.h>

	static int init(void)
	{
		asm volatile("sub    $0x4,%rsp");
		dump_stack();
		asm volatile("add    $0x4,%rsp");

		return -EAGAIN;
	}

	module_init(init);
	MODULE_LICENSE("GPL");

crashes the kernel.

Fixes: e335bb51cc15 ("x86/unwind: Ensure stack pointer is aligned")
Signed-off-by: Vernon Lovejoy <vlovejoy@xxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230512104232.GA10227@xxxxxxxxxx
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 arch/x86/kernel/dumpstack.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 0bf6779..f18ca44 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -195,7 +195,6 @@ static 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);
 
 	/*
@@ -214,9 +213,13 @@ static void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
 	 * - hardirq stack
 	 * - entry stack
 	 */
-	for ( ; stack; stack = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
+	for (stack = stack ?: get_stack_pointer(task, regs);
+	     stack;
+	     stack = stack_info.next_sp) {
 		const char *stack_name;
 
+		stack = PTR_ALIGN(stack, sizeof(long));
+
 		if (get_stack_info(stack, task, &stack_info, &visit_mask)) {
 			/*
 			 * We weren't on a valid stack.  It's possible that