Re: [PATCH RFC v2 14/21] kasan: add and integrate kasan boot parameters

From: Andrey Konovalov
Date: Fri Oct 30 2020 - 15:31:56 EST

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In reply to: Dmitry Vyukov: "Re: [PATCH RFC v2 14/21] kasan: add and integrate kasan boot parameters"
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On Wed, Oct 28, 2020 at 1:27 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>
> On Thu, Oct 22, 2020 at 3:19 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
> >
> > TODO: no meaningful description here yet, please see the cover letter
> > for this RFC series.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> > Link: https://linux-review.googlesource.com/id/If7d37003875b2ed3e0935702c8015c223d6416a4
> > ---
> > mm/kasan/common.c | 92 +++++++++++++-----------
> > mm/kasan/generic.c | 5 ++
> > mm/kasan/hw_tags.c | 169 ++++++++++++++++++++++++++++++++++++++++++++-
> > mm/kasan/kasan.h | 9 +++
> > mm/kasan/report.c | 14 +++-
> > mm/kasan/sw_tags.c | 5 ++
> > 6 files changed, 250 insertions(+), 44 deletions(-)
> >
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index 1a5e6c279a72..cc129ef62ab1 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -129,35 +129,37 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> > unsigned int redzone_size;
> > int redzone_adjust;
> >
> > - /* Add alloc meta. */
> > - cache->kasan_info.alloc_meta_offset = *size;
> > - *size += sizeof(struct kasan_alloc_meta);
> > -
> > - /* Add free meta. */
> > - if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
> > - (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
> > - cache->object_size < sizeof(struct kasan_free_meta))) {
> > - cache->kasan_info.free_meta_offset = *size;
> > - *size += sizeof(struct kasan_free_meta);
> > - }
> > -
> > - redzone_size = optimal_redzone(cache->object_size);
> > - redzone_adjust = redzone_size - (*size - cache->object_size);
> > - if (redzone_adjust > 0)
> > - *size += redzone_adjust;
> > -
> > - *size = min_t(unsigned int, KMALLOC_MAX_SIZE,
> > - max(*size, cache->object_size + redzone_size));
> > + if (static_branch_unlikely(&kasan_stack)) {
>
> Initially I thought kasan_stack is related to stack instrumentation.
> And then wondered why we check it during slab creation.
> I suggest giving it a slightly longer and more descriptive name.

Will do.

> ... reading code further, it also disables quarantine, right?
> Something to mention somewhere.

Quarantine is not supported for anything but generic KASAN. Maybe it
makes sense to put this into documentation...

> > + /* Add alloc meta. */
> > + cache->kasan_info.alloc_meta_offset = *size;
> > + *size += sizeof(struct kasan_alloc_meta);
> > +
> > + /* Add free meta. */
> > + if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
> > + (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
> > + cache->object_size < sizeof(struct kasan_free_meta))) {
> > + cache->kasan_info.free_meta_offset = *size;
> > + *size += sizeof(struct kasan_free_meta);
> > + }
> >
> > - /*
> > - * If the metadata doesn't fit, don't enable KASAN at all.
> > - */
> > - if (*size <= cache->kasan_info.alloc_meta_offset ||
> > - *size <= cache->kasan_info.free_meta_offset) {
> > - cache->kasan_info.alloc_meta_offset = 0;
> > - cache->kasan_info.free_meta_offset = 0;
> > - *size = orig_size;
> > - return;
> > + redzone_size = optimal_redzone(cache->object_size);
> > + redzone_adjust = redzone_size - (*size - cache->object_size);
> > + if (redzone_adjust > 0)
> > + *size += redzone_adjust;
> > +
> > + *size = min_t(unsigned int, KMALLOC_MAX_SIZE,
> > + max(*size, cache->object_size + redzone_size));
> > +
> > + /*
> > + * If the metadata doesn't fit, don't enable KASAN at all.
> > + */
> > + if (*size <= cache->kasan_info.alloc_meta_offset ||
> > + *size <= cache->kasan_info.free_meta_offset) {
> > + cache->kasan_info.alloc_meta_offset = 0;
> > + cache->kasan_info.free_meta_offset = 0;
> > + *size = orig_size;
> > + return;
> > + }
> > }
> >
> > *flags |= SLAB_KASAN;
> > @@ -165,10 +167,12 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> >
> > size_t kasan_metadata_size(struct kmem_cache *cache)
> > {
> > - return (cache->kasan_info.alloc_meta_offset ?
> > - sizeof(struct kasan_alloc_meta) : 0) +
> > - (cache->kasan_info.free_meta_offset ?
> > - sizeof(struct kasan_free_meta) : 0);
> > + if (static_branch_unlikely(&kasan_stack))
> > + return (cache->kasan_info.alloc_meta_offset ?
> > + sizeof(struct kasan_alloc_meta) : 0) +
> > + (cache->kasan_info.free_meta_offset ?
> > + sizeof(struct kasan_free_meta) : 0);
> > + return 0;
> > }
> >
> > struct kasan_alloc_meta *kasan_get_alloc_meta(struct kmem_cache *cache,
> > @@ -270,8 +274,10 @@ void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
> > if (!(cache->flags & SLAB_KASAN))
> > return (void *)object;
> >
> > - alloc_meta = kasan_get_alloc_meta(cache, object);
> > - __memset(alloc_meta, 0, sizeof(*alloc_meta));
> > + if (static_branch_unlikely(&kasan_stack)) {
>
> Interestingly, now SLAB_KASAN is always set when kasan_stack is not
> enabled. So it seems to me we can move the SLAB_KASAN check into this
> unlikely branch now.

Yes, will fix. I'll also include a complete rework of SLAB_KASAN into
the next version.

>
> > + alloc_meta = kasan_get_alloc_meta(cache, object);
> > + __memset(alloc_meta, 0, sizeof(*alloc_meta));
> > + }
> >
> > if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
> > object = set_tag(object, assign_tag(cache, object, true, false));
> > @@ -308,15 +314,19 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
> > rounded_up_size = round_up(cache->object_size, KASAN_GRANULE_SIZE);
> > kasan_poison_memory(object, rounded_up_size, KASAN_KMALLOC_FREE);
> >
> > - if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
> > - unlikely(!(cache->flags & SLAB_KASAN)))
> > - return false;
> > + if (static_branch_unlikely(&kasan_stack)) {
> > + if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
> > + unlikely(!(cache->flags & SLAB_KASAN)))
> > + return false;
> > +
> > + kasan_set_free_info(cache, object, tag);
> >
> > - kasan_set_free_info(cache, object, tag);
> > + quarantine_put(cache, object);
> >
> > - quarantine_put(cache, object);
> > + return IS_ENABLED(CONFIG_KASAN_GENERIC);
> > + }
> >
> > - return IS_ENABLED(CONFIG_KASAN_GENERIC);
> > + return false;
> > }
> >
> > bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
> > @@ -355,7 +365,7 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
> > kasan_poison_memory((void *)redzone_start, redzone_end - redzone_start,
> > KASAN_KMALLOC_REDZONE);
> >
> > - if (cache->flags & SLAB_KASAN)
> > + if (static_branch_unlikely(&kasan_stack) && (cache->flags & SLAB_KASAN))
> > set_alloc_info(cache, (void *)object, flags);
> >
> > return set_tag(object, tag);
> > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> > index d259e4c3aefd..20a1e753e0c5 100644
> > --- a/mm/kasan/generic.c
> > +++ b/mm/kasan/generic.c
> > @@ -33,6 +33,11 @@
> > #include "kasan.h"
> > #include "../slab.h"
> >
> > +/* See the comments in hw_tags.c */
> > +DEFINE_STATIC_KEY_TRUE_RO(kasan_enabled);
> > +EXPORT_SYMBOL(kasan_enabled);
> > +DEFINE_STATIC_KEY_TRUE_RO(kasan_stack);
> > +
> > /*
> > * All functions below always inlined so compiler could
> > * perform better optimizations in each of __asan_loadX/__assn_storeX
> > diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> > index 915142da6b57..bccd781011ad 100644
> > --- a/mm/kasan/hw_tags.c
> > +++ b/mm/kasan/hw_tags.c
> > @@ -8,6 +8,8 @@
> >
> > #define pr_fmt(fmt) "kasan: " fmt
> >
> > +#include <linux/init.h>
> > +#include <linux/jump_label.h>
> > #include <linux/kasan.h>
> > #include <linux/kernel.h>
> > #include <linux/memory.h>
> > @@ -17,10 +19,175 @@
> >
> > #include "kasan.h"
> >
> > +enum kasan_arg_mode {
> > + KASAN_ARG_MODE_OFF,
> > + KASAN_ARG_MODE_PROD,
> > + KASAN_ARG_MODE_FULL,
> > +};
> > +
> > +enum kasan_arg_stack {
> > + KASAN_ARG_STACK_DEFAULT,
> > + KASAN_ARG_STACK_OFF,
> > + KASAN_ARG_STACK_ON,
> > +};
> > +
> > +enum kasan_arg_trap {
> > + KASAN_ARG_TRAP_DEFAULT,
> > + KASAN_ARG_TRAP_ASYNC,
> > + KASAN_ARG_TRAP_SYNC,
> > +};
> > +
> > +enum kasan_arg_fault {
> > + KASAN_ARG_FAULT_DEFAULT,
> > + KASAN_ARG_FAULT_REPORT,
> > + KASAN_ARG_FAULT_PANIC,
> > +};
> > +
> > +static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
> > +static enum kasan_arg_stack kasan_arg_stack __ro_after_init;
> > +static enum kasan_arg_fault kasan_arg_fault __ro_after_init;
> > +static enum kasan_arg_trap kasan_arg_trap __ro_after_init;
> > +
> > +/* Whether KASAN is enabled at all. */
> > +DEFINE_STATIC_KEY_FALSE_RO(kasan_enabled);
> > +EXPORT_SYMBOL(kasan_enabled);
> > +
> > +/* Whether to collect alloc/free stack traces. */
> > +DEFINE_STATIC_KEY_FALSE_RO(kasan_stack);
> > +
> > +/* Whether to use synchronous or asynchronous tag checking. */
> > +static bool kasan_sync __ro_after_init;
> > +
> > +/* Whether panic or disable tag checking on fault. */
> > +bool kasan_panic __ro_after_init;
> > +
> > +/* kasan.mode=off/prod/full */
> > +static int __init early_kasan_mode(char *arg)
> > +{
> > + if (!arg)
> > + return -EINVAL;
> > +
> > + if (!strcmp(arg, "off"))
> > + kasan_arg_mode = KASAN_ARG_MODE_OFF;
> > + else if (!strcmp(arg, "prod"))
> > + kasan_arg_mode = KASAN_ARG_MODE_PROD;
> > + else if (!strcmp(arg, "full"))
> > + kasan_arg_mode = KASAN_ARG_MODE_FULL;
> > + else
> > + return -EINVAL;
> > +
> > + return 0;
> > +}
> > +early_param("kasan.mode", early_kasan_mode);
> > +
> > +/* kasan.stack=off/on */
> > +static int __init early_kasan_stack(char *arg)
> > +{
> > + if (!arg)
> > + return -EINVAL;
> > +
> > + if (!strcmp(arg, "off"))
> > + kasan_arg_stack = KASAN_ARG_STACK_OFF;
> > + else if (!strcmp(arg, "on"))
> > + kasan_arg_stack = KASAN_ARG_STACK_ON;
> > + else
> > + return -EINVAL;
> > +
> > + return 0;
> > +}
> > +early_param("kasan.stack", early_kasan_stack);
> > +
> > +/* kasan.trap=sync/async */
> > +static int __init early_kasan_trap(char *arg)
> > +{
> > + if (!arg)
> > + return -EINVAL;
> > +
> > + if (!strcmp(arg, "ASYNC"))
> > + kasan_arg_trap = KASAN_ARG_TRAP_ASYNC;
> > + else if (!strcmp(arg, "sync"))
> > + kasan_arg_trap = KASAN_ARG_TRAP_SYNC;
> > + else
> > + return -EINVAL;
> > +
> > + return 0;
> > +}
> > +early_param("kasan.trap", early_kasan_trap);
> > +
> > +/* kasan.fault=report/panic */
> > +static int __init early_kasan_fault(char *arg)
> > +{
> > + if (!arg)
> > + return -EINVAL;
> > +
> > + if (!strcmp(arg, "report"))
> > + kasan_arg_fault = KASAN_ARG_FAULT_REPORT;
> > + else if (!strcmp(arg, "panic"))
> > + kasan_arg_fault = KASAN_ARG_FAULT_PANIC;
> > + else
> > + return -EINVAL;
> > +
> > + return 0;
> > +}
> > +early_param("kasan.fault", early_kasan_fault);
> > +
> > void __init kasan_init_tags(void)
> > {
> > - init_tags(KASAN_TAG_MAX);
> > + if (!cpu_supports_tags())
> > + return;
> > +
> > + /* First, preset values based on the mode. */
> > +
> > + switch (kasan_arg_mode) {
> > + case KASAN_ARG_MODE_OFF:
> > + return;
> > + case KASAN_ARG_MODE_PROD:
> > + static_branch_enable(&kasan_enabled);
> > + break;
> > + case KASAN_ARG_MODE_FULL:
> > + static_branch_enable(&kasan_enabled);
> > + static_branch_enable(&kasan_stack);
> > + kasan_sync = true;
> > + break;
> > + }
> > +
> > + /* Now, optionally override the presets. */
> >
> > + switch (kasan_arg_stack) {
> > + case KASAN_ARG_STACK_OFF:
> > + static_branch_disable(&kasan_stack);
> > + break;
> > + case KASAN_ARG_STACK_ON:
> > + static_branch_enable(&kasan_stack);
> > + break;
> > + default:
> > + break;
> > + }
> > +
> > + switch (kasan_arg_trap) {
> > + case KASAN_ARG_TRAP_ASYNC:
> > + kasan_sync = false;
> > + break;
> > + case KASAN_ARG_TRAP_SYNC:
> > + kasan_sync = true;
> > + break;
> > + default:
> > + break;
> > + }
> > +
> > + switch (kasan_arg_fault) {
> > + case KASAN_ARG_FAULT_REPORT:
> > + kasan_panic = false;
> > + break;
> > + case KASAN_ARG_FAULT_PANIC:
> > + kasan_panic = true;
> > + break;
> > + default:
> > + break;
> > + }
> > +
> > + /* TODO: choose between sync and async based on kasan_sync. */
> > + init_tags(KASAN_TAG_MAX);
> > pr_info("KernelAddressSanitizer initialized\n");
> > }
> >
> > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> > index f7ae0c23f023..00b47bc753aa 100644
> > --- a/mm/kasan/kasan.h
> > +++ b/mm/kasan/kasan.h
> > @@ -2,9 +2,18 @@
> > #ifndef __MM_KASAN_KASAN_H
> > #define __MM_KASAN_KASAN_H
> >
> > +#include <linux/jump_label.h>
> > #include <linux/kasan.h>
> > #include <linux/stackdepot.h>
> >
> > +#ifdef CONFIG_KASAN_HW_TAGS
> > +DECLARE_STATIC_KEY_FALSE(kasan_stack);
> > +#else
> > +DECLARE_STATIC_KEY_TRUE(kasan_stack);
> > +#endif
>
> kasan_stack and kasan_enabled make sense and changed only in hw_tags mode.
> It would be cleaner (and faster for other modes) to abstract static keys as:
>
> #ifdef CONFIG_KASAN_HW_TAGS
> #include <linux/jump_label.h>
> DECLARE_STATIC_KEY_FALSE(kasan_stack);
> static inline bool kasan_stack_collection_enabled()
> {
> return static_branch_unlikely(&kasan_stack);
> }
> #else
> static inline bool kasan_stack_collection_enabled() { return true; }
> #endif
>
> This way we don't need to include and define static keys for other modes.

Sounds good, will do.

>
> > +extern bool kasan_panic __ro_after_init;
> > +
> > #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
> > #define KASAN_GRANULE_SIZE (1UL << KASAN_SHADOW_SCALE_SHIFT)
> > #else
> > diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> > index dee5350b459c..426dd1962d3c 100644
> > --- a/mm/kasan/report.c
> > +++ b/mm/kasan/report.c
> > @@ -97,6 +97,10 @@ static void end_report(unsigned long *flags)
> > panic_on_warn = 0;
> > panic("panic_on_warn set ...\n");
> > }
> > +#ifdef CONFIG_KASAN_HW_TAGS
> > + if (kasan_panic)
> > + panic("kasan.fault=panic set ...\n");
> > +#endif
> > kasan_enable_current();
> > }
> >
> > @@ -159,8 +163,8 @@ static void describe_object_addr(struct kmem_cache *cache, void *object,
> > (void *)(object_addr + cache->object_size));
> > }
> >
> > -static void describe_object(struct kmem_cache *cache, void *object,
> > - const void *addr, u8 tag)
> > +static void describe_object_stacks(struct kmem_cache *cache, void *object,
> > + const void *addr, u8 tag)
> > {
> > struct kasan_alloc_meta *alloc_meta = kasan_get_alloc_meta(cache, object);
> >
> > @@ -188,7 +192,13 @@ static void describe_object(struct kmem_cache *cache, void *object,
> > }
> > #endif
> > }
> > +}
> >
> > +static void describe_object(struct kmem_cache *cache, void *object,
> > + const void *addr, u8 tag)
> > +{
> > + if (static_branch_unlikely(&kasan_stack))
> > + describe_object_stacks(cache, object, addr, tag);
> > describe_object_addr(cache, object, addr);
> > }
> >
> > diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> > index 4db41f274702..b6d185adf2c5 100644
> > --- a/mm/kasan/sw_tags.c
> > +++ b/mm/kasan/sw_tags.c
> > @@ -33,6 +33,11 @@
> > #include "kasan.h"
> > #include "../slab.h"
> >
> > +/* See the comments in hw_tags.c */
> > +DEFINE_STATIC_KEY_TRUE_RO(kasan_enabled);
> > +EXPORT_SYMBOL(kasan_enabled);
> > +DEFINE_STATIC_KEY_TRUE_RO(kasan_stack);
> > +
> > static DEFINE_PER_CPU(u32, prng_state);
> >
> > void __init kasan_init_tags(void)
> > --
> > 2.29.0.rc1.297.gfa9743e501-goog
> >

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