3 files changed, 72 insertions, 3 deletions

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 5e82488f1b82..f42fd9e33981 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -47,6 +47,9 @@ int main(void)
   DEFINE(THREAD_KEYS_USER,	offsetof(struct task_struct, thread.keys_user));
   DEFINE(THREAD_KEYS_KERNEL,	offsetof(struct task_struct, thread.keys_kernel));
 #endif
+#ifdef CONFIG_ARM64_MTE
+  DEFINE(THREAD_GCR_EL1_USER,	offsetof(struct task_struct, thread.gcr_user_excl));
+#endif
   BLANK();
   DEFINE(S_X0,			offsetof(struct pt_regs, regs[0]));
   DEFINE(S_X2,			offsetof(struct pt_regs, regs[2]));
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 51c762156099..2a93fa5f4e49 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -173,6 +173,43 @@ alternative_else_nop_endif
 #endif
 	.endm
 
+	.macro mte_set_gcr, tmp, tmp2
+#ifdef CONFIG_ARM64_MTE
+	/*
+	 * 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
+#endif
+	.endm
+
+	.macro mte_set_kernel_gcr, tmp, tmp2
+#ifdef CONFIG_KASAN_HW_TAGS
+alternative_if_not ARM64_MTE
+	b	1f
+alternative_else_nop_endif
+	ldr_l	\tmp, gcr_kernel_excl
+
+	mte_set_gcr \tmp, \tmp2
+1:
+#endif
+	.endm
+
+	.macro mte_set_user_gcr, tsk, tmp, tmp2
+#ifdef CONFIG_ARM64_MTE
+alternative_if_not ARM64_MTE
+	b	1f
+alternative_else_nop_endif
+	ldr	\tmp, [\tsk, #THREAD_GCR_EL1_USER]
+
+	mte_set_gcr \tmp, \tmp2
+1:
+#endif
+	.endm
+
 	.macro	kernel_entry, el, regsize = 64
 	.if	\regsize == 32
 	mov	w0, w0				// zero upper 32 bits of x0
@@ -212,6 +249,8 @@ alternative_else_nop_endif
 
 	ptrauth_keys_install_kernel tsk, x20, x22, x23
 
+	mte_set_kernel_gcr x22, x23
+
 	scs_load tsk, x20
 	.else
 	add	x21, sp, #S_FRAME_SIZE
@@ -315,6 +354,8 @@ 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_set_user_gcr tsk, x0, x1
+
 	apply_ssbd 0, x0, x1
 	.endif
 
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 2e1b1d14c0db..dc9ada64feed 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -23,6 +23,8 @@
 #include <asm/ptrace.h>
 #include <asm/sysreg.h>
 
+u64 gcr_kernel_excl __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);
@@ -129,6 +131,26 @@ void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
 	return ptr;
 }
 
+void mte_init_tags(u64 max_tag)
+{
+	static bool gcr_kernel_excl_initialized;
+
+	if (!gcr_kernel_excl_initialized) {
+		/*
+		 * The format of the tags in KASAN is 0xFF and in MTE is 0xF.
+		 * This conversion extracts an MTE tag from a KASAN tag.
+		 */
+		u64 incl = GENMASK(FIELD_GET(MTE_TAG_MASK >> MTE_TAG_SHIFT,
+					     max_tag), 0);
+
+		gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
+		gcr_kernel_excl_initialized = true;
+	}
+
+	/* Enable the kernel exclude mask for random tags generation. */
+	write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
+}
+
 void mte_enable_kernel(void)
 {
 	/* Enable MTE Sync Mode for EL1. */
@@ -171,7 +193,11 @@ static void update_gcr_el1_excl(u64 excl)
 static void set_gcr_el1_excl(u64 excl)
 {
 	current->thread.gcr_user_excl = excl;
-	update_gcr_el1_excl(excl);
+
+	/*
+	 * SYS_GCR_EL1 will be set to current->thread.gcr_user_excl value
+	 * by mte_set_user_gcr() in kernel_exit,
+	 */
 }
 
 void flush_mte_state(void)
@@ -197,7 +223,6 @@ void mte_thread_switch(struct task_struct *next)
 	/* avoid expensive SCTLR_EL1 accesses if no change */
 	if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0)
 		update_sctlr_el1_tcf0(next->thread.sctlr_tcf0);
-	update_gcr_el1_excl(next->thread.gcr_user_excl);
 }
 
 void mte_suspend_exit(void)
@@ -205,7 +230,7 @@ void mte_suspend_exit(void)
 	if (!system_supports_mte())
 		return;
 
-	update_gcr_el1_excl(current->thread.gcr_user_excl);
+	update_gcr_el1_excl(gcr_kernel_excl);
 }
 
 long set_mte_ctrl(struct task_struct *task, unsigned long arg)