Messages in this thread | | | Date | Thu, 8 Sep 2022 11:36:42 +0100 | Subject | Re: [PATCH v2] mte: Initialize tag storage to KASAN_TAG_INVALID | From | Vladimir Murzin <> |
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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/ ?
> > 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()
> + 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
Anyway, you might want to advertise tag value used for initialization.
> +} > + > 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
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