2019-12-02 11:42:08

by Heyi Guo

Subject: [PATCH] arm64/kernel/entry: refine comment of stack overflow check

Stack overflow checking can be done by testing
sp & (1 << THREAD_SHIFT)
only for the stacks are aligned to (2 << THREAD_SHIFT) with size of
(1 << THREAD_SIZE), and this is the case when CONFIG_VMAP_STACK is
set.

Fix the code comment to avoid confusion.

Signed-off-by: Heyi Guo <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
---
arch/arm64/kernel/entry.S | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index cf3bd2976e57..9e8ba507090f 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -76,7 +76,8 @@ alternative_else_nop_endif
#ifdef CONFIG_VMAP_STACK
/*
* Test whether the SP has overflowed, without corrupting a GPR.
- * Task and IRQ stacks are aligned to (1 << THREAD_SHIFT).
+ * Task and IRQ stacks are aligned to (2 << THREAD_SHIFT) with size of
+ * (1 << THREAD_SHIFT).
*/
add sp, sp, x0 // sp' = sp + x0
sub x0, sp, x0 // x0' = sp' - x0 = (sp + x0) - x0 = sp
--
2.19.1

2019-12-02 12:37:47

by Mark Rutland

Subject: Re: [PATCH] arm64/kernel/entry: refine comment of stack overflow check

On Mon, Dec 02, 2019 at 07:37:02PM +0800, Heyi Guo wrote:
> Stack overflow checking can be done by testing
> sp & (1 << THREAD_SHIFT)
> only for the stacks are aligned to (2 << THREAD_SHIFT) with size of
> (1 << THREAD_SIZE), and this is the case when CONFIG_VMAP_STACK is
> set.

Good point, I was sloppy with this comment.

>
> Fix the code comment to avoid confusion.
>
> Signed-off-by: Heyi Guo <[email protected]>
> Cc: Catalin Marinas <[email protected]>
> Cc: Will Deacon <[email protected]>
> ---
> arch/arm64/kernel/entry.S | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index cf3bd2976e57..9e8ba507090f 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -76,7 +76,8 @@ alternative_else_nop_endif
> #ifdef CONFIG_VMAP_STACK
> /*
> * Test whether the SP has overflowed, without corrupting a GPR.
> - * Task and IRQ stacks are aligned to (1 << THREAD_SHIFT).
> + * Task and IRQ stacks are aligned to (2 << THREAD_SHIFT) with size of
> + * (1 << THREAD_SHIFT).
> */

Can we make that:

Task and IRQ stacks are aligned so that SP & (1 << THREAD_SHIFT)
should always be zero.

... which I think is a bit clearer.

With that wording:

Acked-by: Mark Rutland <[email protected]>

Mark.

> add sp, sp, x0 // sp' = sp + x0
> sub x0, sp, x0 // x0' = sp' - x0 = (sp + x0) - x0 = sp
> --
> 2.19.1
>

2019-12-03 00:56:49

by Heyi Guo

Subject: Re: [PATCH] arm64/kernel/entry: refine comment of stack overflow check

?? 2019/12/2 20:33, Mark Rutland д??:
> On Mon, Dec 02, 2019 at 07:37:02PM +0800, Heyi Guo wrote:
>> Stack overflow checking can be done by testing
>> sp & (1 << THREAD_SHIFT)
>> only for the stacks are aligned to (2 << THREAD_SHIFT) with size of
>> (1 << THREAD_SIZE), and this is the case when CONFIG_VMAP_STACK is
>> set.
> Good point, I was sloppy with this comment.
>
>> Fix the code comment to avoid confusion.
>>
>> Signed-off-by: Heyi Guo <[email protected]>
>> Cc: Catalin Marinas <[email protected]>
>> Cc: Will Deacon <[email protected]>
>> ---
>> arch/arm64/kernel/entry.S | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>> index cf3bd2976e57..9e8ba507090f 100644
>> --- a/arch/arm64/kernel/entry.S
>> +++ b/arch/arm64/kernel/entry.S
>> @@ -76,7 +76,8 @@ alternative_else_nop_endif
>> #ifdef CONFIG_VMAP_STACK
>> /*
>> * Test whether the SP has overflowed, without corrupting a GPR.
>> - * Task and IRQ stacks are aligned to (1 << THREAD_SHIFT).
>> + * Task and IRQ stacks are aligned to (2 << THREAD_SHIFT) with size of
>> + * (1 << THREAD_SHIFT).
>> */
> Can we make that:
>
> Task and IRQ stacks are aligned so that SP & (1 << THREAD_SHIFT)
> should always be zero.
>
> ... which I think is a bit clearer.

Sure :)

Thanks,

Heyi

>
> With that wording:
>
> Acked-by: Mark Rutland <[email protected]>
>
> Mark.
>
>> add sp, sp, x0 // sp' = sp + x0
>> sub x0, sp, x0 // x0' = sp' - x0 = (sp + x0) - x0 = sp
>> --
>> 2.19.1
>>
> .

2019-12-06 13:59:19

by Catalin Marinas

Subject: Re: [PATCH] arm64/kernel/entry: refine comment of stack overflow check

On Mon, Dec 02, 2019 at 07:37:02PM +0800, Heyi Guo wrote:
> Stack overflow checking can be done by testing
> sp & (1 << THREAD_SHIFT)
> only for the stacks are aligned to (2 << THREAD_SHIFT) with size of
> (1 << THREAD_SIZE), and this is the case when CONFIG_VMAP_STACK is
> set.
>
> Fix the code comment to avoid confusion.
>
> Signed-off-by: Heyi Guo <[email protected]>
> Cc: Catalin Marinas <[email protected]>
> Cc: Will Deacon <[email protected]>

Queued with Mark's suggested update.

--
Catalin