On Fri, Aug 14, 2020 at 07:27:06PM +0200, Andrey Konovalov wrote:
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index cde127508e38..a17fefb0571b 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -172,6 +172,29 @@ alternative_else_nop_endif
> #endif
> .endm
>
> + /* Note: tmp should always be a callee-saved register */
Why callee-saved? Do you preserve it anywhere here?
> + .macro mte_restore_gcr, el, tsk, tmp, tmp2
> +#ifdef CONFIG_ARM64_MTE
> +alternative_if_not ARM64_MTE
> + b 1f
> +alternative_else_nop_endif
> + .if \el == 0
> + ldr \tmp, [\tsk, #THREAD_GCR_EL1_USER]
> + .else
> + ldr_l \tmp, gcr_kernel_excl
> + .endif
> + /*
> + * Calculate and set the exclude mask preserving
> + * the RRND (bit[16]) setting.
> + */
> + mrs_s \tmp2, SYS_GCR_EL1
> + bfi \tmp2, \tmp, #0, #16
> + msr_s SYS_GCR_EL1, \tmp2
> + isb
> +1:
> +#endif
> + .endm
> +
> .macro kernel_entry, el, regsize = 64
> .if \regsize == 32
> mov w0, w0 // zero upper 32 bits of x0
> @@ -209,6 +232,8 @@ alternative_else_nop_endif
>
> ptrauth_keys_install_kernel tsk, x20, x22, x23
>
> + mte_restore_gcr 1, tsk, x22, x23
> +
> scs_load tsk, x20
> .else
> add x21, sp, #S_FRAME_SIZE
> @@ -386,6 +411,8 @@ alternative_else_nop_endif
> /* No kernel C function calls after this as user keys are set. */
> ptrauth_keys_install_user tsk, x0, x1, x2
>
> + mte_restore_gcr 0, tsk, x0, x1
> +
> apply_ssbd 0, x0, x1
> .endif
>
> @@ -957,6 +984,7 @@ SYM_FUNC_START(cpu_switch_to)
> mov sp, x9
> msr sp_el0, x1
> ptrauth_keys_install_kernel x1, x8, x9, x10
> + mte_restore_gcr 1, x1, x8, x9
> scs_save x0, x8
> scs_load x1, x8
> ret
Since we set GCR_EL1 on exception entry and return, why is this needed?
We don't have a per-kernel thread GCR_EL1, it's global to all threads,
so I think cpu_switch_to() should not be touched.
> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> index 7717ea9bc2a7..cfac7d02f032 100644
> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -18,10 +18,14 @@
>
> #include <asm/barrier.h>
> #include <asm/cpufeature.h>
> +#include <asm/kasan.h>
> +#include <asm/kprobes.h>
> #include <asm/mte.h>
> #include <asm/ptrace.h>
> #include <asm/sysreg.h>
>
> +u64 gcr_kernel_excl __read_mostly;
Could we make this __ro_after_init?
> +
> static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)
> {
> pte_t old_pte = READ_ONCE(*ptep);
> @@ -115,6 +119,13 @@ void * __must_check mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
> return ptr;
> }
>
> +void mte_init_tags(u64 max_tag)
> +{
> + u64 incl = ((1ULL << ((max_tag & MTE_TAG_MAX) + 1)) - 1);
I'd rather use GENMASK here, it is more readable.
--
Catalin
