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 53de044e565406f5213a105fdefa2a12ebadbd11..92b33c7eaf3f9d1dddcfe1440d7d4bb6acca752b 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