x86/show_trace_log_lvl: Ensure stack pointer is aligned, again

commit 2e4be0d011f21593c6b316806779ba1eba2cd7e0 upstream.

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@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20230512104232.GA10227@redhat.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 0bf6779187dda158a8deba21e14215d2b0cbddb7..f18ca44c904b747e68a3fdf0f7926a7025da71b7 100644 (file)
--- 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