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 2b17a5cec0997c01afa6b778a6a4713c5284d34c..7e698c45760cf1c1e440a22ebba246de6e8da8e7 100644 (file)
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -171,7 +171,6 @@ 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);
 
        /*
@@ -190,9 +189,13 @@ 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