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charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, Aug 18, 2025 at 9:51=E2=80=AFAM Yeoreum Yun w= rote: > > Since Armv8.9, FEATURE_MTE_STORE_ONLY feature is introduced to restrict > raise of tag check fault on store operation only. > Introcude KASAN write only mode based on this feature. > > KASAN write only mode restricts KASAN checks operation for write only and > omits the checks for fetch/read operations when accessing memory. > So it might be used not only debugging enviroment but also normal > enviroment to check memory safty. > > This features can be controlled with "kasan.write_only" arguments. > When "kasan.write_only=3Don", KASAN checks write operation only otherwise > KASAN checks all operations. > > This changes the MTE_STORE_ONLY feature as BOOT_CPU_FEATURE like > ARM64_MTE_ASYMM so that makes it initialise in kasan_init_hw_tags() > with other function together. > > Signed-off-by: Yeoreum Yun > --- > Documentation/dev-tools/kasan.rst | 3 ++ > arch/arm64/include/asm/memory.h | 1 + > arch/arm64/include/asm/mte-kasan.h | 6 ++++ > arch/arm64/kernel/cpufeature.c | 2 +- > arch/arm64/kernel/mte.c | 18 ++++++++++ > mm/kasan/hw_tags.c | 54 ++++++++++++++++++++++++++++-- > mm/kasan/kasan.h | 7 ++++ > 7 files changed, 88 insertions(+), 3 deletions(-) > > diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/= kasan.rst > index 0a1418ab72fd..fe1a1e152275 100644 > --- a/Documentation/dev-tools/kasan.rst > +++ b/Documentation/dev-tools/kasan.rst > @@ -143,6 +143,9 @@ disabling KASAN altogether or controlling its feature= s: > Asymmetric mode: a bad access is detected synchronously on reads and > asynchronously on writes. > > +- ``kasan.write_only=3Doff`` or ``kasan.write_only=3Don`` controls wheth= er KASAN > + checks the write (store) accesses only or all accesses (default: ``off= ``) > + > - ``kasan.vmalloc=3Doff`` or ``=3Don`` disables or enables tagging of vm= alloc > allocations (default: ``on``). > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/mem= ory.h > index 5213248e081b..f1505c4acb38 100644 > --- a/arch/arm64/include/asm/memory.h > +++ b/arch/arm64/include/asm/memory.h > @@ -308,6 +308,7 @@ static inline const void *__tag_set(const void *addr,= u8 tag) > #define arch_enable_tag_checks_sync() mte_enable_kernel_sync() > #define arch_enable_tag_checks_async() mte_enable_kernel_async() > #define arch_enable_tag_checks_asymm() mte_enable_kernel_asymm() > +#define arch_enable_tag_checks_write_only() mte_enable_kernel_store_o= nly() > #define arch_suppress_tag_checks_start() mte_enable_tco() > #define arch_suppress_tag_checks_stop() mte_disable_tco() > #define arch_force_async_tag_fault() mte_check_tfsr_exit() > diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/= mte-kasan.h > index 2e98028c1965..0f9b08e8fb8d 100644 > --- a/arch/arm64/include/asm/mte-kasan.h > +++ b/arch/arm64/include/asm/mte-kasan.h > @@ -200,6 +200,7 @@ static inline void mte_set_mem_tag_range(void *addr, = size_t size, u8 tag, > void mte_enable_kernel_sync(void); > void mte_enable_kernel_async(void); > void mte_enable_kernel_asymm(void); > +int mte_enable_kernel_store_only(void); > > #else /* CONFIG_ARM64_MTE */ > > @@ -251,6 +252,11 @@ static inline void mte_enable_kernel_asymm(void) > { > } > > +static inline int mte_enable_kernel_store_only(void) > +{ > + return -EINVAL; > +} > + > #endif /* CONFIG_ARM64_MTE */ > > #endif /* __ASSEMBLY__ */ > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeatur= e.c > index 9ad065f15f1d..505bd56e21a2 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -2920,7 +2920,7 @@ static const struct arm64_cpu_capabilities arm64_fe= atures[] =3D { > { > .desc =3D "Store Only MTE Tag Check", > .capability =3D ARM64_MTE_STORE_ONLY, > - .type =3D ARM64_CPUCAP_SYSTEM_FEATURE, > + .type =3D ARM64_CPUCAP_BOOT_CPU_FEATURE, > .matches =3D has_cpuid_feature, > ARM64_CPUID_FIELDS(ID_AA64PFR2_EL1, MTESTOREONLY, IMP) > }, > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index e5e773844889..cd5452eb7486 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -157,6 +157,24 @@ void mte_enable_kernel_asymm(void) > mte_enable_kernel_sync(); > } > } > + > +int mte_enable_kernel_store_only(void) > +{ > + /* > + * If the CPU does not support MTE store only, > + * the kernel checks all operations. > + */ > + if (!cpus_have_cap(ARM64_MTE_STORE_ONLY)) > + return -EINVAL; > + > + sysreg_clear_set(sctlr_el1, SCTLR_EL1_TCSO_MASK, > + SYS_FIELD_PREP(SCTLR_EL1, TCSO, 1)); > + isb(); > + > + pr_info_once("MTE: enabled stonly mode at EL1\n"); > + > + return 0; > +} > #endif > > #ifdef CONFIG_KASAN_HW_TAGS > diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c > index 9a6927394b54..df67b48739b4 100644 > --- a/mm/kasan/hw_tags.c > +++ b/mm/kasan/hw_tags.c > @@ -41,9 +41,16 @@ enum kasan_arg_vmalloc { > KASAN_ARG_VMALLOC_ON, > }; > > +enum kasan_arg_write_only { > + KASAN_ARG_WRITE_ONLY_DEFAULT, > + KASAN_ARG_WRITE_ONLY_OFF, > + KASAN_ARG_WRITE_ONLY_ON, > +}; > + > static enum kasan_arg kasan_arg __ro_after_init; > static enum kasan_arg_mode kasan_arg_mode __ro_after_init; > static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata; > +static enum kasan_arg_write_only kasan_arg_write_only __ro_after_init; > > /* > * Whether KASAN is enabled at all. > @@ -67,6 +74,8 @@ DEFINE_STATIC_KEY_FALSE(kasan_flag_vmalloc); > #endif > EXPORT_SYMBOL_GPL(kasan_flag_vmalloc); > > +static bool kasan_flag_write_only; > + > #define PAGE_ALLOC_SAMPLE_DEFAULT 1 > #define PAGE_ALLOC_SAMPLE_ORDER_DEFAULT 3 > > @@ -141,6 +150,23 @@ static int __init early_kasan_flag_vmalloc(char *arg= ) > } > early_param("kasan.vmalloc", early_kasan_flag_vmalloc); > > +/* kasan.write_only=3Doff/on */ > +static int __init early_kasan_flag_write_only(char *arg) > +{ > + if (!arg) > + return -EINVAL; > + > + if (!strcmp(arg, "off")) > + kasan_arg_write_only =3D KASAN_ARG_WRITE_ONLY_OFF; > + else if (!strcmp(arg, "on")) > + kasan_arg_write_only =3D KASAN_ARG_WRITE_ONLY_ON; > + else > + return -EINVAL; > + > + return 0; > +} > +early_param("kasan.write_only", early_kasan_flag_write_only); > + > static inline const char *kasan_mode_info(void) > { > if (kasan_mode =3D=3D KASAN_MODE_ASYNC) > @@ -257,15 +283,26 @@ void __init kasan_init_hw_tags(void) > break; > } > > + switch (kasan_arg_write_only) { > + case KASAN_ARG_WRITE_ONLY_DEFAULT: Let's keep this part similar to the other parameters for consistency: /* Default is specified by kasan_flag_write_only definition. */ break; > + case KASAN_ARG_WRITE_ONLY_OFF: > + kasan_flag_write_only =3D false; > + break; > + case KASAN_ARG_WRITE_ONLY_ON: > + kasan_flag_write_only =3D true; > + break; > + } > + > kasan_init_tags(); > > /* KASAN is now initialized, enable it. */ > static_branch_enable(&kasan_flag_enabled); > > - pr_info("KernelAddressSanitizer initialized (hw-tags, mode=3D%s, = vmalloc=3D%s, stacktrace=3D%s)\n", > + pr_info("KernelAddressSanitizer initialized (hw-tags, mode=3D%s, = vmalloc=3D%s, stacktrace=3D%s, write_only=3D%s\n", > kasan_mode_info(), > str_on_off(kasan_vmalloc_enabled()), > - str_on_off(kasan_stack_collection_enabled())); > + str_on_off(kasan_stack_collection_enabled()), > + str_on_off(kasan_arg_write_only)); > } > > #ifdef CONFIG_KASAN_VMALLOC > @@ -392,6 +429,13 @@ void kasan_enable_hw_tags(void) > hw_enable_tag_checks_asymm(); > else > hw_enable_tag_checks_sync(); > + > + if (kasan_arg_write_only =3D=3D KASAN_ARG_WRITE_ONLY_ON && We already set kasan_flag_write_only by this point, right? Let's check that one then. > + hw_enable_tag_checks_write_only()) { > + kasan_arg_write_only =3D=3D KASAN_ARG_WRITE_ONLY_OFF; Typo in =3D=3D in the line above. But also I think we can just drop the line: kasan_arg_write_only is KASAN_ARG_WRITE_ONLY_ON after all, it's just not supported and thus kasan_flag_write_only is set to false to reflect that. > + kasan_flag_write_only =3D false; > + pr_warn_once("System doesn't support write-only option. D= isable it\n"); Let's do pr_err like the rest of KASAN code. And: pr_err_once("write-only mode is not supported and thus not enabled\n"); > + } > } > > #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST) > @@ -404,4 +448,10 @@ VISIBLE_IF_KUNIT void kasan_force_async_fault(void) > } > EXPORT_SYMBOL_IF_KUNIT(kasan_force_async_fault); > > +VISIBLE_IF_KUNIT bool kasan_write_only_enabled(void) > +{ > + return kasan_flag_write_only; > +} > +EXPORT_SYMBOL_IF_KUNIT(kasan_write_only_enabled); > + > #endif > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h > index 129178be5e64..c1490136c96b 100644 > --- a/mm/kasan/kasan.h > +++ b/mm/kasan/kasan.h > @@ -428,6 +428,7 @@ static inline const void *arch_kasan_set_tag(const vo= id *addr, u8 tag) > #define hw_enable_tag_checks_sync() arch_enable_tag_checks_sy= nc() > #define hw_enable_tag_checks_async() arch_enable_tag_checks_as= ync() > #define hw_enable_tag_checks_asymm() arch_enable_tag_checks_as= ymm() > +#define hw_enable_tag_checks_write_only() arch_enable_tag_checks_wr= ite_only() > #define hw_suppress_tag_checks_start() arch_suppress_tag_checks_= start() > #define hw_suppress_tag_checks_stop() arch_suppress_tag_checks_= stop() > #define hw_force_async_tag_fault() arch_force_async_tag_faul= t() > @@ -437,11 +438,17 @@ static inline const void *arch_kasan_set_tag(const = void *addr, u8 tag) > arch_set_mem_tag_range((addr), (size), (tag), (in= it)) > > void kasan_enable_hw_tags(void); > +bool kasan_write_only_enabled(void); This should go next to kasan_force_async_fault(). > > #else /* CONFIG_KASAN_HW_TAGS */ > > static inline void kasan_enable_hw_tags(void) { } > > +static inline bool kasan_write_only_enabled(void) > +{ > + return false; > +} And this too. > + > #endif /* CONFIG_KASAN_HW_TAGS */ > > #if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS) > -- > LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7} >