On 2/9/21 11:35 AM, Catalin Marinas wrote:
> 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.
>
Good point, increases clarity. I will add it in the next version.
>> +
>> 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().
>
Ok, will do in the next version.
>> __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.
>
Indeed, as you are saying at the moment is done at boot only but it is better to
make the code more future proof. Maybe with a note in the commit message.
--
Regards,
Vincenzo
