Factor out the code that fills the stack with the stackleak poison value
in order to allow architectures to provide a faster implementation.
Acked-by: Vasily Gorbik <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>
---
kernel/stackleak.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/kernel/stackleak.c b/kernel/stackleak.c
index c2c33d2202e9..34c9d81eea94 100644
--- a/kernel/stackleak.c
+++ b/kernel/stackleak.c
@@ -70,6 +70,18 @@ late_initcall(stackleak_sysctls_init);
#define skip_erasing() false
#endif /* CONFIG_STACKLEAK_RUNTIME_DISABLE */
+#ifndef __stackleak_poison
+static __always_inline void __stackleak_poison(unsigned long erase_low,
+ unsigned long erase_high,
+ unsigned long poison)
+{
+ while (erase_low < erase_high) {
+ *(unsigned long *)erase_low = poison;
+ erase_low += sizeof(unsigned long);
+ }
+}
+#endif
+
static __always_inline void __stackleak_erase(bool on_task_stack)
{
const unsigned long task_stack_low = stackleak_task_low_bound(current);
@@ -101,10 +113,7 @@ static __always_inline void __stackleak_erase(bool on_task_stack)
else
erase_high = task_stack_high;
- while (erase_low < erase_high) {
- *(unsigned long *)erase_low = STACKLEAK_POISON;
- erase_low += sizeof(unsigned long);
- }
+ __stackleak_poison(erase_low, erase_high, STACKLEAK_POISON);
/* Reset the 'lowest_stack' value for the next syscall */
current->lowest_stack = task_stack_high;
--
2.37.2
On Wed, Apr 05, 2023 at 03:08:40PM +0200, Heiko Carstens wrote:
> Factor out the code that fills the stack with the stackleak poison value
> in order to allow architectures to provide a faster implementation.
>
> Acked-by: Vasily Gorbik <[email protected]>
> Signed-off-by: Heiko Carstens <[email protected]>
As on patch 2, it might be nicer to have a noinstr-safe memset64() and use that
directly, but I don't have strong feelings either way, and I'll defer to Kees's
judgement:
Acked-by: Mark Rutland <[email protected]>
Thanks,
Mark.
> ---
> kernel/stackleak.c | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/stackleak.c b/kernel/stackleak.c
> index c2c33d2202e9..34c9d81eea94 100644
> --- a/kernel/stackleak.c
> +++ b/kernel/stackleak.c
> @@ -70,6 +70,18 @@ late_initcall(stackleak_sysctls_init);
> #define skip_erasing() false
> #endif /* CONFIG_STACKLEAK_RUNTIME_DISABLE */
>
> +#ifndef __stackleak_poison
> +static __always_inline void __stackleak_poison(unsigned long erase_low,
> + unsigned long erase_high,
> + unsigned long poison)
> +{
> + while (erase_low < erase_high) {
> + *(unsigned long *)erase_low = poison;
> + erase_low += sizeof(unsigned long);
> + }
> +}
> +#endif
> +
> static __always_inline void __stackleak_erase(bool on_task_stack)
> {
> const unsigned long task_stack_low = stackleak_task_low_bound(current);
> @@ -101,10 +113,7 @@ static __always_inline void __stackleak_erase(bool on_task_stack)
> else
> erase_high = task_stack_high;
>
> - while (erase_low < erase_high) {
> - *(unsigned long *)erase_low = STACKLEAK_POISON;
> - erase_low += sizeof(unsigned long);
> - }
> + __stackleak_poison(erase_low, erase_high, STACKLEAK_POISON);
>
> /* Reset the 'lowest_stack' value for the next syscall */
> current->lowest_stack = task_stack_high;
> --
> 2.37.2
>
On Wed, Apr 12, 2023 at 10:03:46AM +0100, Mark Rutland wrote:
> On Wed, Apr 05, 2023 at 03:08:40PM +0200, Heiko Carstens wrote:
> > Factor out the code that fills the stack with the stackleak poison value
> > in order to allow architectures to provide a faster implementation.
> >
> > Acked-by: Vasily Gorbik <[email protected]>
> > Signed-off-by: Heiko Carstens <[email protected]>
>
> As on patch 2, it might be nicer to have a noinstr-safe memset64() and use that
> directly, but I don't have strong feelings either way, and I'll defer to Kees's
> judgement:
Wouldn't that enforce that memset64() wouldn't be allowed to have an own
stackframe, since otherwise it would write poison values to it, since we
have
if (on_task_stack)
erase_high = current_stack_pointer;
in __stackleak_erase()?
That was actually my motiviation to make this s390 optimization an always
inline asm.
Besides that this wouldn't be a problem for at least s390, since memset64()
is an asm function which comes whithout the need for a stackframe, but on
the other hand this would add a quite subtle requirement to memset64(), if
I'm not mistaken.
On Wed, Apr 12, 2023 at 11:58:07AM +0200, Heiko Carstens wrote:
> On Wed, Apr 12, 2023 at 10:03:46AM +0100, Mark Rutland wrote:
> > On Wed, Apr 05, 2023 at 03:08:40PM +0200, Heiko Carstens wrote:
> > > Factor out the code that fills the stack with the stackleak poison value
> > > in order to allow architectures to provide a faster implementation.
> > >
> > > Acked-by: Vasily Gorbik <[email protected]>
> > > Signed-off-by: Heiko Carstens <[email protected]>
> >
> > As on patch 2, it might be nicer to have a noinstr-safe memset64() and use that
> > directly, but I don't have strong feelings either way, and I'll defer to Kees's
> > judgement:
>
> Wouldn't that enforce that memset64() wouldn't be allowed to have an own
> stackframe, since otherwise it would write poison values to it, since we
> have
>
> if (on_task_stack)
> erase_high = current_stack_pointer;
>
> in __stackleak_erase()?
Yes, sorry -- I was implicitly assuming that a noinstr-safe version would be
__always_inline.
> That was actually my motiviation to make this s390 optimization an always
> inline asm.
>
> Besides that this wouldn't be a problem for at least s390, since memset64()
> is an asm function which comes whithout the need for a stackframe, but on
> the other hand this would add a quite subtle requirement to memset64(), if
> I'm not mistaken.
That's a fair enough justification, I think. Thanks for the details!
Thanks,
Mark.