From: Vernon Lovejoy <[email protected]>
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 <[email protected]>
Signed-off-by: Oleg Nesterov <[email protected]>
---
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 0bf6779187dd..f18ca44c904b 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
--
2.25.1.362.g51ebf55
Josh, this is boring.
We are changing this simple fix for the second time, precisely following
your recommendations. And for the second time, you mysteriously disappear
afterward.
Please tell us if you finally agree with this version or if you think we
should make changes again.
Thanks.
On 05/12, Oleg Nesterov wrote:
>
> From: Vernon Lovejoy <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Oleg Nesterov <[email protected]>
> ---
> 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 0bf6779187dd..f18ca44c904b 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
> --
> 2.25.1.362.g51ebf55
>
On Mon, May 15, 2023 at 08:26:08PM +0200, Oleg Nesterov wrote:
> Josh, this is boring.
>
> We are changing this simple fix for the second time, precisely following
> your recommendations. And for the second time, you mysteriously disappear
> afterward.
Patience, please. I'm not just sitting around waiting for your patches.
> Please tell us if you finally agree with this version or if you think we
> should make changes again.
Looks fine.
Acked-by: Josh Poimboeuf <[email protected]>
--
Josh
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 <[email protected]>
AuthorDate: Fri, 12 May 2023 12:42:32 +02:00
Committer: Josh Poimboeuf <[email protected]>
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 <[email protected]>
Signed-off-by: Oleg Nesterov <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Josh Poimboeuf <[email protected]>
---
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