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 b4964300153a1ae6d43bba564af7ae5b2bf8b52e..b9736aac20eef6ab9049b5fc495b62654180477e 100644 (file)
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -195,7 +195,6 @@ 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 @@ 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