Messages in this thread Patch in this message |  | | Date | Tue, 9 Feb 2021 11:35:06 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH v12 4/7] arm64: mte: Enable TCO in functions that can read beyond buffer limits |
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On Mon, Feb 08, 2021 at 04:56:14PM +0000, Vincenzo Frascino wrote: > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > index 0deb88467111..f43d78aee593 100644 > --- a/arch/arm64/include/asm/uaccess.h > +++ b/arch/arm64/include/asm/uaccess.h > @@ -188,6 +188,21 @@ static inline void __uaccess_enable_tco(void) > ARM64_MTE, CONFIG_KASAN_HW_TAGS)); > } > > +/* Whether the MTE asynchronous mode is enabled. */ > +DECLARE_STATIC_KEY_FALSE(mte_async_mode); > + > +static inline void __uaccess_disable_tco_async(void) > +{ > + if (static_branch_unlikely(&mte_async_mode)) > + __uaccess_disable_tco(); > +} > + > +static inline void __uaccess_enable_tco_async(void) > +{ > + if (static_branch_unlikely(&mte_async_mode)) > + __uaccess_enable_tco(); > +}
I would add a comment here along the lines of what's in the commit log: these functions disable tag checking only if in MTE async mode since the sync mode generates exceptions synchronously and the nofault or load_unaligned_zeropad can handle them.
> + > static inline void uaccess_disable_privileged(void) > { > __uaccess_disable_tco(); > @@ -307,8 +322,10 @@ do { \ > do { \ > int __gkn_err = 0; \ > \ > + __uaccess_enable_tco_async(); \ > __raw_get_mem("ldr", *((type *)(dst)), \ > (__force type *)(src), __gkn_err); \ > + __uaccess_disable_tco_async(); \ > if (unlikely(__gkn_err)) \ > goto err_label; \ > } while (0) > @@ -379,9 +396,11 @@ do { \ > #define __put_kernel_nofault(dst, src, type, err_label) \ > do { \ > int __pkn_err = 0; \ > + __uaccess_enable_tco_async(); \ > \
Nitpick: for consistency with the __get_kernel_nofault() function, please move the empty line above __uaccess_enable_tco_async().
> __raw_put_mem("str", *((type *)(src)), \ > (__force type *)(dst), __pkn_err); \ > + __uaccess_disable_tco_async(); \ > if (unlikely(__pkn_err)) \ > goto err_label; \ > } while(0)
[...]
> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index 92078e1eb627..60531afc706e 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -27,6 +27,10 @@ u64 gcr_kernel_excl __ro_after_init; > > static bool report_fault_once = true; > > +/* Whether the MTE asynchronous mode is enabled. */ > +DEFINE_STATIC_KEY_FALSE(mte_async_mode); > +EXPORT_SYMBOL_GPL(mte_async_mode); > + > static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > { > pte_t old_pte = READ_ONCE(*ptep); > @@ -170,6 +174,12 @@ void mte_enable_kernel_sync(void) > void mte_enable_kernel_async(void) > { > __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC); > + > + /* > + * This function is called on each active smp core, we do not > + * to take cpu_hotplug_lock again. > + */ > + static_branch_enable_cpuslocked(&mte_async_mode); > }
Do we need to disable mte_async_mode in mte_enable_kernel_sync()? I think currently that's only done at boot time but kasan may gain some run-time features and change the mode dynamically.
-- Catalin
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