On 8/27/20 11:38 AM, Catalin Marinas wrote:
On Fri, Aug 14, 2020 at 07:27:06PM +0200, Andrey Konovalov wrote:
quoted
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?
Aargh, this is an old comment, I forgot to remove it after the last refactor.
Thank you for pointing this out.
quoted
+ .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.
I agree, we can remove it. We only require the kernel entry and the kernel exit
ones.
quoted
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?
Yes, it makes sense, it should be updated only once through mte_init_tags().
Something to consider though here is that this might not be the right approach
if in future we want to add stack tagging. In such a case we need to know the
kernel exclude mask before any C code is executed. Initializing the mask via
mte_init_tags() it is too late.
I was thinking to add a compilation define instead of having gcr_kernel_excl in
place. This might not work if the kernel excl mask is meant to change during the
execution.
Thoughts?
quoted
+
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.
Agree, we can change it.
--
Regards,
Vincenzo
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel