* Re: [PATCH] kasan, scs: collect stack traces from shadow stack
2022-03-12 20:14 [PATCH] kasan, scs: collect stack traces from shadow stack andrey.konovalov
@ 2022-03-13 16:59 ` Andrey Konovalov
2022-03-13 23:44 ` Andrey Konovalov
` (2 subsequent siblings)
3 siblings, 0 replies; 9+ messages in thread
From: Andrey Konovalov @ 2022-03-13 16:59 UTC (permalink / raw)
To: andrey.konovalov
Cc: Marco Elver, Alexander Potapenko, Andrew Morton, Dmitry Vyukov,
Andrey Ryabinin, kasan-dev, Vincenzo Frascino, Catalin Marinas,
Will Deacon, Mark Rutland, Sami Tolvanen, Peter Collingbourne,
Evgenii Stepanov, Linux Memory Management List, LKML,
Andrey Konovalov, Florian Mayer
On Sat, Mar 12, 2022 at 9:14 PM <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> Currently, KASAN always uses the normal stack trace collection routines,
> which rely on the unwinder, when saving alloc and free stack traces.
>
> Instead of invoking the unwinder, collect the stack trace by copying
> frames from the Shadow Call Stack whenever it is enabled. This reduces
> boot time by 30% for all KASAN modes when Shadow Call Stack is enabled.
>
> To avoid potentially leaking PAC pointer tags, strip them when saving
> the stack trace.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> ---
>
> Things to consider:
>
> We could integrate shadow stack trace collection into kernel/stacktrace.c
> as e.g. stack_trace_save_shadow(). However, using stack_trace_consume_fn
> leads to invoking a callback on each saved from, which is undesirable.
> The plain copy loop is faster.
>
> We could add a command line flag to switch between stack trace collection
> modes. I noticed that Shadow Call Stack might be missing certain frames
> in stacks originating from a fault that happens in the middle of a
> function. I am not sure if this case is important to handle though.
>
> Looking forward to thoughts and comments.
>
> Thanks!
>
> ---
> mm/kasan/common.c | 36 +++++++++++++++++++++++++++++++++++-
> 1 file changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index d9079ec11f31..65a0723370c7 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -9,6 +9,7 @@
> * Andrey Konovalov <andreyknvl@gmail.com>
> */
>
> +#include <linux/bits.h>
> #include <linux/export.h>
> #include <linux/init.h>
> #include <linux/kasan.h>
> @@ -21,6 +22,7 @@
> #include <linux/printk.h>
> #include <linux/sched.h>
> #include <linux/sched/task_stack.h>
> +#include <linux/scs.h>
> #include <linux/slab.h>
> #include <linux/stacktrace.h>
> #include <linux/string.h>
> @@ -30,12 +32,44 @@
> #include "kasan.h"
> #include "../slab.h"
>
> +#ifdef CONFIG_SHADOW_CALL_STACK
> +
> +#ifdef CONFIG_ARM64_PTR_AUTH
> +#define PAC_TAG_RESET(x) (x | GENMASK(63, CONFIG_ARM64_VA_BITS))
> +#else
> +#define PAC_TAG_RESET(x) (x)
> +#endif
> +
> +static unsigned int save_shadow_stack(unsigned long *entries,
> + unsigned int nr_entries)
> +{
> + unsigned long *scs_sp = task_scs_sp(current);
> + unsigned long *scs_base = task_scs(current);
> + unsigned long *frame;
> + unsigned int i = 0;
> +
> + for (frame = scs_sp - 1; frame >= scs_base; frame--) {
> + entries[i++] = PAC_TAG_RESET(*frame);
> + if (i >= nr_entries)
> + break;
> + }
> +
> + return i;
> +}
> +#else /* CONFIG_SHADOW_CALL_STACK */
> +static inline unsigned int save_shadow_stack(unsigned long *entries,
> + unsigned int nr_entries) { return 0; }
> +#endif /* CONFIG_SHADOW_CALL_STACK */
> +
> depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
> {
> unsigned long entries[KASAN_STACK_DEPTH];
> unsigned int nr_entries;
>
> - nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> + if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK))
> + nr_entries = save_shadow_stack(entries, ARRAY_SIZE(entries));
> + else
> + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> return __stack_depot_save(entries, nr_entries, flags, can_alloc);
> }
>
> --
> 2.25.1
>
CC Florian
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] kasan, scs: collect stack traces from shadow stack
2022-03-12 20:14 [PATCH] kasan, scs: collect stack traces from shadow stack andrey.konovalov
2022-03-13 16:59 ` Andrey Konovalov
@ 2022-03-13 23:44 ` Andrey Konovalov
2022-03-14 8:57 ` Marco Elver
2022-03-14 7:00 ` Marco Elver
2022-03-14 7:17 ` Dmitry Vyukov
3 siblings, 1 reply; 9+ messages in thread
From: Andrey Konovalov @ 2022-03-13 23:44 UTC (permalink / raw)
To: andrey.konovalov
Cc: Marco Elver, Alexander Potapenko, Andrew Morton, Dmitry Vyukov,
Andrey Ryabinin, kasan-dev, Vincenzo Frascino, Catalin Marinas,
Will Deacon, Mark Rutland, Sami Tolvanen, Peter Collingbourne,
Evgenii Stepanov, Linux Memory Management List, LKML,
Andrey Konovalov, Florian Mayer
On Sat, Mar 12, 2022 at 9:14 PM <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> Currently, KASAN always uses the normal stack trace collection routines,
> which rely on the unwinder, when saving alloc and free stack traces.
>
> Instead of invoking the unwinder, collect the stack trace by copying
> frames from the Shadow Call Stack whenever it is enabled. This reduces
> boot time by 30% for all KASAN modes when Shadow Call Stack is enabled.
>
> To avoid potentially leaking PAC pointer tags, strip them when saving
> the stack trace.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> ---
>
> Things to consider:
>
> We could integrate shadow stack trace collection into kernel/stacktrace.c
> as e.g. stack_trace_save_shadow(). However, using stack_trace_consume_fn
> leads to invoking a callback on each saved from, which is undesirable.
> The plain copy loop is faster.
>
> We could add a command line flag to switch between stack trace collection
> modes. I noticed that Shadow Call Stack might be missing certain frames
> in stacks originating from a fault that happens in the middle of a
> function. I am not sure if this case is important to handle though.
>
> Looking forward to thoughts and comments.
>
> Thanks!
>
> ---
> mm/kasan/common.c | 36 +++++++++++++++++++++++++++++++++++-
> 1 file changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index d9079ec11f31..65a0723370c7 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -9,6 +9,7 @@
> * Andrey Konovalov <andreyknvl@gmail.com>
> */
>
> +#include <linux/bits.h>
> #include <linux/export.h>
> #include <linux/init.h>
> #include <linux/kasan.h>
> @@ -21,6 +22,7 @@
> #include <linux/printk.h>
> #include <linux/sched.h>
> #include <linux/sched/task_stack.h>
> +#include <linux/scs.h>
> #include <linux/slab.h>
> #include <linux/stacktrace.h>
> #include <linux/string.h>
> @@ -30,12 +32,44 @@
> #include "kasan.h"
> #include "../slab.h"
>
> +#ifdef CONFIG_SHADOW_CALL_STACK
> +
> +#ifdef CONFIG_ARM64_PTR_AUTH
> +#define PAC_TAG_RESET(x) (x | GENMASK(63, CONFIG_ARM64_VA_BITS))
> +#else
> +#define PAC_TAG_RESET(x) (x)
> +#endif
> +
> +static unsigned int save_shadow_stack(unsigned long *entries,
> + unsigned int nr_entries)
> +{
> + unsigned long *scs_sp = task_scs_sp(current);
> + unsigned long *scs_base = task_scs(current);
> + unsigned long *frame;
> + unsigned int i = 0;
> +
> + for (frame = scs_sp - 1; frame >= scs_base; frame--) {
> + entries[i++] = PAC_TAG_RESET(*frame);
> + if (i >= nr_entries)
> + break;
> + }
> +
> + return i;
> +}
> +#else /* CONFIG_SHADOW_CALL_STACK */
> +static inline unsigned int save_shadow_stack(unsigned long *entries,
> + unsigned int nr_entries) { return 0; }
> +#endif /* CONFIG_SHADOW_CALL_STACK */
> +
> depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
> {
> unsigned long entries[KASAN_STACK_DEPTH];
> unsigned int nr_entries;
>
> - nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> + if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK))
> + nr_entries = save_shadow_stack(entries, ARRAY_SIZE(entries));
> + else
> + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> return __stack_depot_save(entries, nr_entries, flags, can_alloc);
Another option here is to instruct stack depot to get the stack from
the Shadow Call Stack. This would avoid copying the frames twice.
> }
>
> --
> 2.25.1
>
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] kasan, scs: collect stack traces from shadow stack
2022-03-13 23:44 ` Andrey Konovalov
@ 2022-03-14 8:57 ` Marco Elver
2022-03-20 21:12 ` Andrey Konovalov
0 siblings, 1 reply; 9+ messages in thread
From: Marco Elver @ 2022-03-14 8:57 UTC (permalink / raw)
To: Andrey Konovalov
Cc: andrey.konovalov, Alexander Potapenko, Andrew Morton,
Dmitry Vyukov, Andrey Ryabinin, kasan-dev, Vincenzo Frascino,
Catalin Marinas, Will Deacon, Mark Rutland, Sami Tolvanen,
Peter Collingbourne, Evgenii Stepanov,
Linux Memory Management List, LKML, Andrey Konovalov,
Florian Mayer
On Mon, 14 Mar 2022 at 00:44, Andrey Konovalov <andreyknvl@gmail.com> wrote:
>
> On Sat, Mar 12, 2022 at 9:14 PM <andrey.konovalov@linux.dev> wrote:
> >
> > From: Andrey Konovalov <andreyknvl@google.com>
> >
> > Currently, KASAN always uses the normal stack trace collection routines,
> > which rely on the unwinder, when saving alloc and free stack traces.
> >
> > Instead of invoking the unwinder, collect the stack trace by copying
> > frames from the Shadow Call Stack whenever it is enabled. This reduces
> > boot time by 30% for all KASAN modes when Shadow Call Stack is enabled.
> >
> > To avoid potentially leaking PAC pointer tags, strip them when saving
> > the stack trace.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> >
> > ---
> >
> > Things to consider:
> >
> > We could integrate shadow stack trace collection into kernel/stacktrace.c
> > as e.g. stack_trace_save_shadow(). However, using stack_trace_consume_fn
> > leads to invoking a callback on each saved from, which is undesirable.
> > The plain copy loop is faster.
> >
> > We could add a command line flag to switch between stack trace collection
> > modes. I noticed that Shadow Call Stack might be missing certain frames
> > in stacks originating from a fault that happens in the middle of a
> > function. I am not sure if this case is important to handle though.
> >
> > Looking forward to thoughts and comments.
> >
> > Thanks!
> >
> > ---
> > mm/kasan/common.c | 36 +++++++++++++++++++++++++++++++++++-
> > 1 file changed, 35 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index d9079ec11f31..65a0723370c7 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -9,6 +9,7 @@
> > * Andrey Konovalov <andreyknvl@gmail.com>
> > */
> >
> > +#include <linux/bits.h>
> > #include <linux/export.h>
> > #include <linux/init.h>
> > #include <linux/kasan.h>
> > @@ -21,6 +22,7 @@
> > #include <linux/printk.h>
> > #include <linux/sched.h>
> > #include <linux/sched/task_stack.h>
> > +#include <linux/scs.h>
> > #include <linux/slab.h>
> > #include <linux/stacktrace.h>
> > #include <linux/string.h>
> > @@ -30,12 +32,44 @@
> > #include "kasan.h"
> > #include "../slab.h"
> >
> > +#ifdef CONFIG_SHADOW_CALL_STACK
> > +
> > +#ifdef CONFIG_ARM64_PTR_AUTH
> > +#define PAC_TAG_RESET(x) (x | GENMASK(63, CONFIG_ARM64_VA_BITS))
> > +#else
> > +#define PAC_TAG_RESET(x) (x)
> > +#endif
> > +
> > +static unsigned int save_shadow_stack(unsigned long *entries,
> > + unsigned int nr_entries)
> > +{
> > + unsigned long *scs_sp = task_scs_sp(current);
> > + unsigned long *scs_base = task_scs(current);
> > + unsigned long *frame;
> > + unsigned int i = 0;
> > +
> > + for (frame = scs_sp - 1; frame >= scs_base; frame--) {
> > + entries[i++] = PAC_TAG_RESET(*frame);
> > + if (i >= nr_entries)
> > + break;
> > + }
> > +
> > + return i;
> > +}
> > +#else /* CONFIG_SHADOW_CALL_STACK */
> > +static inline unsigned int save_shadow_stack(unsigned long *entries,
> > + unsigned int nr_entries) { return 0; }
> > +#endif /* CONFIG_SHADOW_CALL_STACK */
> > +
> > depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
> > {
> > unsigned long entries[KASAN_STACK_DEPTH];
> > unsigned int nr_entries;
> >
> > - nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> > + if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK))
> > + nr_entries = save_shadow_stack(entries, ARRAY_SIZE(entries));
> > + else
> > + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> > return __stack_depot_save(entries, nr_entries, flags, can_alloc);
>
> Another option here is to instruct stack depot to get the stack from
> the Shadow Call Stack. This would avoid copying the frames twice.
Yes, I think a stack_depot_save_shadow() would be appropriate if it
saves a copy.
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] kasan, scs: collect stack traces from shadow stack
2022-03-14 8:57 ` Marco Elver
@ 2022-03-20 21:12 ` Andrey Konovalov
0 siblings, 0 replies; 9+ messages in thread
From: Andrey Konovalov @ 2022-03-20 21:12 UTC (permalink / raw)
To: Marco Elver
Cc: andrey.konovalov, Alexander Potapenko, Andrew Morton,
Dmitry Vyukov, Andrey Ryabinin, kasan-dev, Vincenzo Frascino,
Catalin Marinas, Will Deacon, Mark Rutland, Sami Tolvanen,
Peter Collingbourne, Evgenii Stepanov,
Linux Memory Management List, LKML, Andrey Konovalov,
Florian Mayer
On Mon, Mar 14, 2022 at 9:57 AM Marco Elver <elver@google.com> wrote:
>
> > Another option here is to instruct stack depot to get the stack from
> > the Shadow Call Stack. This would avoid copying the frames twice.
>
> Yes, I think a stack_depot_save_shadow() would be appropriate if it
> saves a copy.
Sounds good, will do in v2.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] kasan, scs: collect stack traces from shadow stack
2022-03-12 20:14 [PATCH] kasan, scs: collect stack traces from shadow stack andrey.konovalov
2022-03-13 16:59 ` Andrey Konovalov
2022-03-13 23:44 ` Andrey Konovalov
@ 2022-03-14 7:00 ` Marco Elver
2022-03-20 21:09 ` Andrey Konovalov
2022-03-14 7:17 ` Dmitry Vyukov
3 siblings, 1 reply; 9+ messages in thread
From: Marco Elver @ 2022-03-14 7:00 UTC (permalink / raw)
To: andrey.konovalov
Cc: Alexander Potapenko, Andrew Morton, Andrey Konovalov,
Dmitry Vyukov, Andrey Ryabinin, kasan-dev, Vincenzo Frascino,
Catalin Marinas, Will Deacon, Mark Rutland, Sami Tolvanen,
Peter Collingbourne, Evgenii Stepanov, linux-mm, linux-kernel,
Andrey Konovalov
On Sat, 12 Mar 2022 at 21:14, <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> Currently, KASAN always uses the normal stack trace collection routines,
> which rely on the unwinder, when saving alloc and free stack traces.
>
> Instead of invoking the unwinder, collect the stack trace by copying
> frames from the Shadow Call Stack whenever it is enabled. This reduces
> boot time by 30% for all KASAN modes when Shadow Call Stack is enabled.
This is impressive.
> To avoid potentially leaking PAC pointer tags, strip them when saving
> the stack trace.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> ---
>
> Things to consider:
>
> We could integrate shadow stack trace collection into kernel/stacktrace.c
> as e.g. stack_trace_save_shadow(). However, using stack_trace_consume_fn
> leads to invoking a callback on each saved from, which is undesirable.
> The plain copy loop is faster.
Why is stack_trace_consume_fn required? This is an internal detail of
arch_stack_walk(), but to implement stack_trace_save_shadow() that's
not used at all.
I think having stack_trace_save_shadow() as you have implemented in
kernel/stacktrace.c or simply in kernel/scs.c itself would be
appropriate.
> We could add a command line flag to switch between stack trace collection
> modes. I noticed that Shadow Call Stack might be missing certain frames
> in stacks originating from a fault that happens in the middle of a
> function. I am not sure if this case is important to handle though.
I think SCS should just work - and if it doesn't, can we fix it? It is
unclear to me what would be a deciding factor to choose between stack
trace collection modes, since it is hard to quantify when and if SCS
doesn't work as intended. So I fear it'd just be an option that's
never used because we don't understand when it's required to be used.
> Looking forward to thoughts and comments.
>
> Thanks!
>
> ---
> mm/kasan/common.c | 36 +++++++++++++++++++++++++++++++++++-
> 1 file changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index d9079ec11f31..65a0723370c7 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -9,6 +9,7 @@
> * Andrey Konovalov <andreyknvl@gmail.com>
> */
>
> +#include <linux/bits.h>
> #include <linux/export.h>
> #include <linux/init.h>
> #include <linux/kasan.h>
> @@ -21,6 +22,7 @@
> #include <linux/printk.h>
> #include <linux/sched.h>
> #include <linux/sched/task_stack.h>
> +#include <linux/scs.h>
> #include <linux/slab.h>
> #include <linux/stacktrace.h>
> #include <linux/string.h>
> @@ -30,12 +32,44 @@
> #include "kasan.h"
> #include "../slab.h"
>
> +#ifdef CONFIG_SHADOW_CALL_STACK
> +
> +#ifdef CONFIG_ARM64_PTR_AUTH
> +#define PAC_TAG_RESET(x) (x | GENMASK(63, CONFIG_ARM64_VA_BITS))
This should go into arch/arm64/include/asm/kasan.h, and here it should
then just do
#ifndef PAC_TAG_RESET
#define ...
> +#else
> +#define PAC_TAG_RESET(x) (x)
> +#endif
But perhaps there's a better, more generic location for this macro?
> +static unsigned int save_shadow_stack(unsigned long *entries,
> + unsigned int nr_entries)
> +{
> + unsigned long *scs_sp = task_scs_sp(current);
> + unsigned long *scs_base = task_scs(current);
> + unsigned long *frame;
> + unsigned int i = 0;
> +
> + for (frame = scs_sp - 1; frame >= scs_base; frame--) {
> + entries[i++] = PAC_TAG_RESET(*frame);
> + if (i >= nr_entries)
> + break;
> + }
> +
> + return i;
> +}
> +#else /* CONFIG_SHADOW_CALL_STACK */
> +static inline unsigned int save_shadow_stack(unsigned long *entries,
> + unsigned int nr_entries) { return 0; }
> +#endif /* CONFIG_SHADOW_CALL_STACK */
> +
> depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
> {
> unsigned long entries[KASAN_STACK_DEPTH];
> unsigned int nr_entries;
>
> - nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> + if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK))
> + nr_entries = save_shadow_stack(entries, ARRAY_SIZE(entries));
> + else
> + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> return __stack_depot_save(entries, nr_entries, flags, can_alloc);
> }
>
> --
> 2.25.1
>
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] kasan, scs: collect stack traces from shadow stack
2022-03-14 7:00 ` Marco Elver
@ 2022-03-20 21:09 ` Andrey Konovalov
0 siblings, 0 replies; 9+ messages in thread
From: Andrey Konovalov @ 2022-03-20 21:09 UTC (permalink / raw)
To: Marco Elver
Cc: andrey.konovalov, Alexander Potapenko, Andrew Morton,
Dmitry Vyukov, Andrey Ryabinin, kasan-dev, Vincenzo Frascino,
Catalin Marinas, Will Deacon, Mark Rutland, Sami Tolvanen,
Peter Collingbourne, Evgenii Stepanov,
Linux Memory Management List, LKML, Andrey Konovalov
On Mon, Mar 14, 2022 at 8:01 AM Marco Elver <elver@google.com> wrote:
>
> > Instead of invoking the unwinder, collect the stack trace by copying
> > frames from the Shadow Call Stack whenever it is enabled. This reduces
> > boot time by 30% for all KASAN modes when Shadow Call Stack is enabled.
>
> This is impressive.
I was surprised too.
> > We could integrate shadow stack trace collection into kernel/stacktrace.c
> > as e.g. stack_trace_save_shadow(). However, using stack_trace_consume_fn
> > leads to invoking a callback on each saved from, which is undesirable.
> > The plain copy loop is faster.
>
> Why is stack_trace_consume_fn required? This is an internal detail of
> arch_stack_walk(), but to implement stack_trace_save_shadow() that's
> not used at all.
>
> I think having stack_trace_save_shadow() as you have implemented in
> kernel/stacktrace.c or simply in kernel/scs.c itself would be
> appropriate.
The other stack trace routines consistently use on
stack_trace_consume_fn. But I think you're right, we don't need it.
Will do in v2.
> > We could add a command line flag to switch between stack trace collection
> > modes. I noticed that Shadow Call Stack might be missing certain frames
> > in stacks originating from a fault that happens in the middle of a
> > function. I am not sure if this case is important to handle though.
>
> I think SCS should just work - and if it doesn't, can we fix it? It is
> unclear to me what would be a deciding factor to choose between stack
> trace collection modes, since it is hard to quantify when and if SCS
> doesn't work as intended. So I fear it'd just be an option that's
> never used because we don't understand when it's required to be used.
Let's just rely on SCS for now and reconsider in case any significant
limitations are discovered.
> > +#ifdef CONFIG_SHADOW_CALL_STACK
> > +
> > +#ifdef CONFIG_ARM64_PTR_AUTH
> > +#define PAC_TAG_RESET(x) (x | GENMASK(63, CONFIG_ARM64_VA_BITS))
>
> This should go into arch/arm64/include/asm/kasan.h, and here it should
> then just do
>
> #ifndef PAC_TAG_RESET
> #define ...
>
>
> > +#else
> > +#define PAC_TAG_RESET(x) (x)
> > +#endif
>
> But perhaps there's a better, more generic location for this macro?
Will move in v2.
Thanks!
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] kasan, scs: collect stack traces from shadow stack
2022-03-12 20:14 [PATCH] kasan, scs: collect stack traces from shadow stack andrey.konovalov
` (2 preceding siblings ...)
2022-03-14 7:00 ` Marco Elver
@ 2022-03-14 7:17 ` Dmitry Vyukov
2022-03-20 21:09 ` Andrey Konovalov
3 siblings, 1 reply; 9+ messages in thread
From: Dmitry Vyukov @ 2022-03-14 7:17 UTC (permalink / raw)
To: andrey.konovalov
Cc: Marco Elver, Alexander Potapenko, Andrew Morton,
Andrey Konovalov, Andrey Ryabinin, kasan-dev, Vincenzo Frascino,
Catalin Marinas, Will Deacon, Mark Rutland, Sami Tolvanen,
Peter Collingbourne, Evgenii Stepanov, linux-mm, linux-kernel,
Andrey Konovalov
On Sat, 12 Mar 2022 at 21:14, <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> Currently, KASAN always uses the normal stack trace collection routines,
> which rely on the unwinder, when saving alloc and free stack traces.
>
> Instead of invoking the unwinder, collect the stack trace by copying
> frames from the Shadow Call Stack whenever it is enabled. This reduces
> boot time by 30% for all KASAN modes when Shadow Call Stack is enabled.
>
> To avoid potentially leaking PAC pointer tags, strip them when saving
> the stack trace.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> ---
>
> Things to consider:
>
> We could integrate shadow stack trace collection into kernel/stacktrace.c
> as e.g. stack_trace_save_shadow(). However, using stack_trace_consume_fn
> leads to invoking a callback on each saved from, which is undesirable.
> The plain copy loop is faster.
>
> We could add a command line flag to switch between stack trace collection
> modes. I noticed that Shadow Call Stack might be missing certain frames
> in stacks originating from a fault that happens in the middle of a
> function. I am not sure if this case is important to handle though.
>
> Looking forward to thoughts and comments.
>
> Thanks!
>
> ---
> mm/kasan/common.c | 36 +++++++++++++++++++++++++++++++++++-
> 1 file changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index d9079ec11f31..65a0723370c7 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -9,6 +9,7 @@
> * Andrey Konovalov <andreyknvl@gmail.com>
> */
>
> +#include <linux/bits.h>
> #include <linux/export.h>
> #include <linux/init.h>
> #include <linux/kasan.h>
> @@ -21,6 +22,7 @@
> #include <linux/printk.h>
> #include <linux/sched.h>
> #include <linux/sched/task_stack.h>
> +#include <linux/scs.h>
> #include <linux/slab.h>
> #include <linux/stacktrace.h>
> #include <linux/string.h>
> @@ -30,12 +32,44 @@
> #include "kasan.h"
> #include "../slab.h"
>
> +#ifdef CONFIG_SHADOW_CALL_STACK
> +
> +#ifdef CONFIG_ARM64_PTR_AUTH
> +#define PAC_TAG_RESET(x) (x | GENMASK(63, CONFIG_ARM64_VA_BITS))
> +#else
> +#define PAC_TAG_RESET(x) (x)
> +#endif
> +
> +static unsigned int save_shadow_stack(unsigned long *entries,
> + unsigned int nr_entries)
> +{
> + unsigned long *scs_sp = task_scs_sp(current);
> + unsigned long *scs_base = task_scs(current);
Just to double-check: interrupt frames are also appended to the the
current task buffer, right?
> + unsigned long *frame;
> + unsigned int i = 0;
> +
> + for (frame = scs_sp - 1; frame >= scs_base; frame--) {
> + entries[i++] = PAC_TAG_RESET(*frame);
> + if (i >= nr_entries)
> + break;
> + }
> +
> + return i;
> +}
> +#else /* CONFIG_SHADOW_CALL_STACK */
> +static inline unsigned int save_shadow_stack(unsigned long *entries,
> + unsigned int nr_entries) { return 0; }
> +#endif /* CONFIG_SHADOW_CALL_STACK */
> +
> depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
> {
> unsigned long entries[KASAN_STACK_DEPTH];
> unsigned int nr_entries;
>
> - nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> + if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK))
> + nr_entries = save_shadow_stack(entries, ARRAY_SIZE(entries));
> + else
> + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> return __stack_depot_save(entries, nr_entries, flags, can_alloc);
> }
>
> --
> 2.25.1
>
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] kasan, scs: collect stack traces from shadow stack
2022-03-14 7:17 ` Dmitry Vyukov
@ 2022-03-20 21:09 ` Andrey Konovalov
0 siblings, 0 replies; 9+ messages in thread
From: Andrey Konovalov @ 2022-03-20 21:09 UTC (permalink / raw)
To: Dmitry Vyukov
Cc: andrey.konovalov, Marco Elver, Alexander Potapenko,
Andrew Morton, Andrey Ryabinin, kasan-dev, Vincenzo Frascino,
Catalin Marinas, Will Deacon, Mark Rutland, Sami Tolvanen,
Peter Collingbourne, Evgenii Stepanov,
Linux Memory Management List, LKML, Andrey Konovalov
On Mon, Mar 14, 2022 at 8:17 AM Dmitry Vyukov <dvyukov@google.com> wrote:
>
> > +static unsigned int save_shadow_stack(unsigned long *entries,
> > + unsigned int nr_entries)
> > +{
> > + unsigned long *scs_sp = task_scs_sp(current);
> > + unsigned long *scs_base = task_scs(current);
>
> Just to double-check: interrupt frames are also appended to the the
> current task buffer, right?
Looked into this and found a few issues, will fix in v2. Interrupt
frames will be collected then.
^ permalink raw reply [flat|nested] 9+ messages in thread