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Message-ID: <CA+fCnZfuu3MLgeSJONqKaXMzkBsGxTQYjTtF0_=fMf4dGGQZCw@mail.gmail.com>
Date: Wed, 6 Oct 2021 14:19:28 +0200
From: Andrey Konovalov <andreyknvl@...il.com>
To: Vincenzo Frascino <vincenzo.frascino@....com>
Cc: Linux ARM <linux-arm-kernel@...ts.infradead.org>,
LKML <linux-kernel@...r.kernel.org>,
kasan-dev <kasan-dev@...glegroups.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Dmitry Vyukov <dvyukov@...gle.com>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Alexander Potapenko <glider@...gle.com>,
Marco Elver <elver@...gle.com>,
Evgenii Stepanov <eugenis@...gle.com>,
Branislav Rankov <Branislav.Rankov@....com>,
Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH v2 5/5] kasan: Extend KASAN mode kernel parameter
On Mon, Oct 4, 2021 at 10:23 PM Vincenzo Frascino
<vincenzo.frascino@....com> wrote:
>
> Architectures supported by KASAN_HW_TAGS can provide an asymmetric mode
> of execution. On an MTE enabled arm64 hw for example this can be
> identified with the asymmetric tagging mode of execution. In particular,
> when such a mode is present, the CPU triggers a fault on a tag mismatch
> during a load operation and asynchronously updates a register when a tag
> mismatch is detected during a store operation.
>
> Extend the KASAN HW execution mode kernel command line parameter to
> support asymmetric mode.
>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Cc: Alexander Potapenko <glider@...gle.com>
> Cc: Andrey Konovalov <andreyknvl@...il.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> ---
> Documentation/dev-tools/kasan.rst | 7 +++++--
> lib/test_kasan.c | 2 +-
> mm/kasan/hw_tags.c | 27 ++++++++++++++++++++++-----
> mm/kasan/kasan.h | 22 +++++++++++++++++++---
> mm/kasan/report.c | 2 +-
> 5 files changed, 48 insertions(+), 12 deletions(-)
>
> diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
> index 21dc03bc10a4..8089c559d339 100644
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -194,14 +194,17 @@ additional boot parameters that allow disabling KASAN or controlling features:
>
> - ``kasan=off`` or ``=on`` controls whether KASAN is enabled (default: ``on``).
>
> -- ``kasan.mode=sync`` or ``=async`` controls whether KASAN is configured in
> - synchronous or asynchronous mode of execution (default: ``sync``).
> +- ``kasan.mode=sync``, ``=async`` or ``=asymm`` controls whether KASAN
> + is configured in synchronous, asynchronous or asymmetric mode of
> + execution (default: ``sync``).
> Synchronous mode: a bad access is detected immediately when a tag
> check fault occurs.
> Asynchronous mode: a bad access detection is delayed. When a tag check
> fault occurs, the information is stored in hardware (in the TFSR_EL1
> register for arm64). The kernel periodically checks the hardware and
> only reports tag faults during these checks.
> + Asymmetric mode: a bad access is detected synchronously on reads and
> + asynchronously on writes.
>
> - ``kasan.stacktrace=off`` or ``=on`` disables or enables alloc and free stack
> traces collection (default: ``on``).
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 8835e0784578..ebed755ebf34 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -88,7 +88,7 @@ static void kasan_test_exit(struct kunit *test)
> */
> #define KUNIT_EXPECT_KASAN_FAIL(test, expression) do { \
> if (IS_ENABLED(CONFIG_KASAN_HW_TAGS) && \
> - !kasan_async_mode_enabled()) \
> + kasan_sync_fault_possible()) \
> migrate_disable(); \
> KUNIT_EXPECT_FALSE(test, READ_ONCE(fail_data.report_found)); \
> barrier(); \
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 05d1e9460e2e..87eb7aa13918 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -29,6 +29,7 @@ enum kasan_arg_mode {
> KASAN_ARG_MODE_DEFAULT,
> KASAN_ARG_MODE_SYNC,
> KASAN_ARG_MODE_ASYNC,
> + KASAN_ARG_MODE_ASYMM,
> };
>
> enum kasan_arg_stacktrace {
> @@ -49,6 +50,10 @@ EXPORT_SYMBOL(kasan_flag_enabled);
> bool kasan_flag_async __ro_after_init;
> EXPORT_SYMBOL_GPL(kasan_flag_async);
>
> +/* Whether the asymmetric mode is enabled. */
> +bool kasan_flag_asymm __ro_after_init;
> +EXPORT_SYMBOL_GPL(kasan_flag_asymm);
> +
> /* Whether to collect alloc/free stack traces. */
> DEFINE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
>
> @@ -69,7 +74,7 @@ static int __init early_kasan_flag(char *arg)
> }
> early_param("kasan", early_kasan_flag);
>
> -/* kasan.mode=sync/async */
> +/* kasan.mode=sync/async/asymm */
> static int __init early_kasan_mode(char *arg)
> {
> if (!arg)
> @@ -79,6 +84,8 @@ static int __init early_kasan_mode(char *arg)
> kasan_arg_mode = KASAN_ARG_MODE_SYNC;
> else if (!strcmp(arg, "async"))
> kasan_arg_mode = KASAN_ARG_MODE_ASYNC;
> + else if (!strcmp(arg, "asymm"))
> + kasan_arg_mode = KASAN_ARG_MODE_ASYMM;
> else
> return -EINVAL;
>
> @@ -116,11 +123,13 @@ void kasan_init_hw_tags_cpu(void)
> return;
>
> /*
> - * Enable async mode only when explicitly requested through
> - * the command line.
> + * Enable async or asymm modes only when explicitly requested
> + * through the command line.
> */
> if (kasan_arg_mode == KASAN_ARG_MODE_ASYNC)
> hw_enable_tagging_async();
> + else if (kasan_arg_mode == KASAN_ARG_MODE_ASYMM)
> + hw_enable_tagging_asymm();
> else
> hw_enable_tagging_sync();
> }
> @@ -143,16 +152,24 @@ void __init kasan_init_hw_tags(void)
> case KASAN_ARG_MODE_DEFAULT:
> /*
> * Default to sync mode.
> - * Do nothing, kasan_flag_async keeps its default value.
> + * Do nothing, kasan_flag_async and kasan_flag_asymm keep
> + * their default values.
> */
> break;
> case KASAN_ARG_MODE_SYNC:
> - /* Do nothing, kasan_flag_async keeps its default value. */
> + /*
> + * Do nothing, kasan_flag_async and kasan_flag_asymm keep
> + * their default values.
> + */
> break;
> case KASAN_ARG_MODE_ASYNC:
> /* Async mode enabled. */
> kasan_flag_async = true;
> break;
> + case KASAN_ARG_MODE_ASYMM:
> + /* Asymm mode enabled. */
> + kasan_flag_asymm = true;
> + break;
> }
>
> switch (kasan_arg_stacktrace) {
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 3639e7c8bb98..1d331ce67dec 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -14,15 +14,21 @@
>
> DECLARE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
> extern bool kasan_flag_async __ro_after_init;
> +extern bool kasan_flag_asymm __ro_after_init;
>
> static inline bool kasan_stack_collection_enabled(void)
> {
> return static_branch_unlikely(&kasan_flag_stacktrace);
> }
>
> -static inline bool kasan_async_mode_enabled(void)
> +static inline bool kasan_async_fault_possible(void)
> {
> - return kasan_flag_async;
> + return kasan_flag_async | kasan_flag_asymm;
> +}
> +
> +static inline bool kasan_sync_fault_possible(void)
> +{
> + return !kasan_flag_async | kasan_flag_asymm;
This should be just !kasan_flag_async.
It seems that choosing one exclusive option out of 3 via two bools is
confusing. How about an enum?
enum kasan_mode {
KASAN_MODE_SYNC,
KASAN_MODE_ASYNC,
KASAN_MODE_ASYMM,
};
enum kasan_mode kasan_mode __ro_after_init;
EXPORT_SYMBOL_GPL(kasan_mode);
I also agree with Marco re using || instead of |.
> }
> #else
>
> @@ -31,11 +37,16 @@ static inline bool kasan_stack_collection_enabled(void)
> return true;
> }
>
> -static inline bool kasan_async_mode_enabled(void)
> +static inline bool kasan_async_fault_possible(void)
> {
> return false;
> }
>
> +static inline bool kasan_sync_fault_possible(void)
> +{
> + return true;
> +}
> +
> #endif
>
> #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
> @@ -287,6 +298,9 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
> #ifndef arch_enable_tagging_async
> #define arch_enable_tagging_async()
> #endif
> +#ifndef arch_enable_tagging_asymm
> +#define arch_enable_tagging_asymm()
> +#endif
> #ifndef arch_force_async_tag_fault
> #define arch_force_async_tag_fault()
> #endif
> @@ -302,6 +316,7 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
>
> #define hw_enable_tagging_sync() arch_enable_tagging_sync()
> #define hw_enable_tagging_async() arch_enable_tagging_async()
> +#define hw_enable_tagging_asymm() arch_enable_tagging_asymm()
> #define hw_force_async_tag_fault() arch_force_async_tag_fault()
> #define hw_get_random_tag() arch_get_random_tag()
> #define hw_get_mem_tag(addr) arch_get_mem_tag(addr)
> @@ -312,6 +327,7 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
>
> #define hw_enable_tagging_sync()
> #define hw_enable_tagging_async()
> +#define hw_enable_tagging_asymm()
>
> #endif /* CONFIG_KASAN_HW_TAGS */
>
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 884a950c7026..9da071ad930c 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -112,7 +112,7 @@ static void start_report(unsigned long *flags)
>
> static void end_report(unsigned long *flags, unsigned long addr)
> {
> - if (!kasan_async_mode_enabled())
> + if (!kasan_async_fault_possible())
> trace_error_report_end(ERROR_DETECTOR_KASAN, addr);
> pr_err("==================================================================\n");
> add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> --
> 2.33.0
>
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