Messages in this thread | | | Date | Thu, 8 Sep 2022 14:49:25 +0100 | Subject | Re: [PATCH v2] mte: Initialize tag storage to KASAN_TAG_INVALID | From | Vincenzo Frascino <> |
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Hi Vladimir,
On 9/8/22 11:36, Vladimir Murzin wrote: > Hi Vincenzo, > > On 9/7/22 12:00, Vincenzo Frascino wrote: >> When the kernel is entered on aarch64, the MTE allocation tags are in an >> UNKNOWN state. >> >> With MTE enabled, the tags are initialized: >> - When a page is allocated and the user maps it with PROT_MTE. >> - On allocation, with in-kernel MTE enabled (HW_TAGS KASAN). >> >> If the tag pool is zeroed by the hardware at reset, it makes it >> difficult to track potential places where the initialization of the >> tags was missed. >> >> This can be observed under QEMU for aarch64, which initializes the MTE >> allocation tags to zero. >> >> Initialize to tag storage to KASAN_TAG_INVALID to catch potential >> places where the initialization of the tags was missed. >> >> This is done introducing a new kernel command line parameter >> "mte.tags_init" that enables the debug option. >> >> Note: The proposed solution should be considered a debug option because >> it might have performance impact on large machines at boot. >> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> >> --- >> arch/arm64/kernel/mte.c | 47 +++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 47 insertions(+) > > Nothing in Documentation/ ? >
I can have a separate patch that adds documentation of the kernel parameter.
>> >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c >> index b2b730233274..af9a8eba9be4 100644 >> --- a/arch/arm64/kernel/mte.c >> +++ b/arch/arm64/kernel/mte.c >> @@ -6,6 +6,7 @@ >> #include <linux/bitops.h> >> #include <linux/cpu.h> >> #include <linux/kernel.h> >> +#include <linux/memblock.h> >> #include <linux/mm.h> >> #include <linux/prctl.h> >> #include <linux/sched.h> >> @@ -35,6 +36,8 @@ DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode); >> EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode); >> #endif >> >> +static bool mte_tags_init __ro_after_init; >> + >> static void mte_sync_page_tags(struct page *page, pte_t old_pte, >> bool check_swap, bool pte_is_tagged) >> { >> @@ -98,6 +101,48 @@ int memcmp_pages(struct page *page1, struct page *page2) >> return ret; >> } >> >> +/* mte.tags_init=off/on */ >> +static int __init early_mte_tags_init(char *arg) >> +{ >> + if (!arg) >> + return -EINVAL; >> + >> + if (!strcmp(arg, "off")) >> + mte_tags_init = false; >> + else if (!strcmp(arg, "on")) >> + mte_tags_init = true; >> + else >> + return -EINVAL; >> + > > You might want to offload parsing to kstrtobool() >
Good point, I was not aware of this API. Thanks!
>> + return 0; >> +} >> +early_param("mte.tags_init", early_mte_tags_init); >> + >> +static inline void __mte_tag_storage_init(void) >> +{ >> + static bool mte_tags_uninitialized = true; >> + phys_addr_t pa_start, pa_end; >> + u64 index; >> + >> + if (mte_tags_init && !mte_tags_uninitialized) >> + return; >> + >> + for_each_mem_range(index, &pa_start, &pa_end) { >> + void *va_start = (void *)__phys_to_virt(pa_start); >> + void *va_end = (void *)__phys_to_virt(pa_end); >> + size_t va_size = (u64)va_end - (u64)va_start; >> + >> + if (va_start >= va_end) >> + break; >> + >> + mte_set_mem_tag_range(va_start, va_size, KASAN_TAG_INVALID, false); >> + } >> + >> + /* Tags are now initialized to KASAN_TAG_INVALID */ >> + mte_tags_uninitialized = false; >> + pr_info("MTE: Tag Storage Initialized\n"); > > Why All Words Start With Capital Letter? :D >
Do you have any preference? :D
> Anyway, you might want to advertise tag value used for initialization. >
Yes I agree, I can print "Tag Storage Initialized to 0x.."
>> +} >> + >> static inline void __mte_enable_kernel(const char *mode, unsigned long tcf) >> { >> /* Enable MTE Sync Mode for EL1. */ >> @@ -105,6 +150,8 @@ static inline void __mte_enable_kernel(const char *mode, unsigned long tcf) >> SYS_FIELD_PREP(SCTLR_EL1, TCF, tcf)); >> isb(); >> >> + __mte_tag_storage_init(); >> + >> pr_info_once("MTE: enabled in %s mode at EL1\n", mode); >> } >> > > Cheers > Vladimir
-- Regards, Vincenzo
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