arm64: mte: convert gcr_user into an exclude mask

The gcr_user mask is a per thread mask that represents the tags that are
excluded from random generation when the Memory Tagging Extension is
present and an 'irg' instruction is invoked.

gcr_user affects the behavior on EL0 only.

Currently that mask is an include mask and it is controlled by the user
via prctl() while GCR_EL1 accepts an exclude mask.

Convert the include mask into an exclude one to make it easier the
register setting.

Note: This change will affect gcr_kernel (for EL1) introduced with a
future patch.

Link: https://lkml.kernel.org/r/946dd31be833b660334c4f93410acf6d6c4cf3c4.1606161801.git.andreyknvl@google.com
Signed-off-by: Vincenzo Frascino <[email protected]>
Signed-off-by: Andrey Konovalov <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Tested-by: Vincenzo Frascino <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Branislav Rankov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Evgenii Stepanov <[email protected]>
Cc: Kevin Brodsky <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

arch/arm64/include/asm/processor.h

@@ -152,7 +152,7 @@ struct thread_struct {
 #endif
 #ifdef CONFIG_ARM64_MTE
 	u64			sctlr_tcf0;
-	u64			gcr_user_incl;
+	u64			gcr_user_excl;
 #endif
 };
 

arch/arm64/kernel/mte.c

@@ -156,23 +156,22 @@ static void set_sctlr_el1_tcf0(u64 tcf0)
 	preempt_enable();
 }
 
-static void update_gcr_el1_excl(u64 incl)
+static void update_gcr_el1_excl(u64 excl)
 {
-	u64 excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
 
 	/*
-	 * Note that 'incl' is an include mask (controlled by the user via
-	 * prctl()) while GCR_EL1 accepts an exclude mask.
+	 * Note that the mask controlled by the user via prctl() is an
+	 * include while GCR_EL1 accepts an exclude mask.
 	 * No need for ISB since this only affects EL0 currently, implicit
 	 * with ERET.
 	 */
 	sysreg_clear_set_s(SYS_GCR_EL1, SYS_GCR_EL1_EXCL_MASK, excl);
 }
 
-static void set_gcr_el1_excl(u64 incl)
+static void set_gcr_el1_excl(u64 excl)
 {
-	current->thread.gcr_user_incl = incl;
-	update_gcr_el1_excl(incl);
+	current->thread.gcr_user_excl = excl;
+	update_gcr_el1_excl(excl);
 }
 
 void flush_mte_state(void)
@@ -187,7 +186,7 @@ void flush_mte_state(void)
 	/* disable tag checking */
 	set_sctlr_el1_tcf0(SCTLR_EL1_TCF0_NONE);
 	/* reset tag generation mask */
-	set_gcr_el1_excl(0);
+	set_gcr_el1_excl(SYS_GCR_EL1_EXCL_MASK);
 }
 
 void mte_thread_switch(struct task_struct *next)
@@ -198,21 +197,22 @@ 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_incl);
+	update_gcr_el1_excl(next->thread.gcr_user_excl);
 }
 
 void mte_suspend_exit(void)
 {
 	if (!system_supports_mte())
 		return;
 
-	update_gcr_el1_excl(current->thread.gcr_user_incl);
+	update_gcr_el1_excl(current->thread.gcr_user_excl);
 }
 
 long set_mte_ctrl(struct task_struct *task, unsigned long arg)
 {
 	u64 tcf0;
-	u64 gcr_incl = (arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT;
+	u64 gcr_excl = ~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) &
+		       SYS_GCR_EL1_EXCL_MASK;
 
 	if (!system_supports_mte())
 		return 0;
@@ -233,10 +233,10 @@ long set_mte_ctrl(struct task_struct *task, unsigned long arg)
 
 	if (task != current) {
 		task->thread.sctlr_tcf0 = tcf0;
-		task->thread.gcr_user_incl = gcr_incl;
+		task->thread.gcr_user_excl = gcr_excl;
 	} else {
 		set_sctlr_el1_tcf0(tcf0);
-		set_gcr_el1_excl(gcr_incl);
+		set_gcr_el1_excl(gcr_excl);
 	}
 
 	return 0;
@@ -245,11 +245,12 @@ long set_mte_ctrl(struct task_struct *task, unsigned long arg)
 long get_mte_ctrl(struct task_struct *task)
 {
 	unsigned long ret;
+	u64 incl = ~task->thread.gcr_user_excl & SYS_GCR_EL1_EXCL_MASK;
 
 	if (!system_supports_mte())
 		return 0;
 
-	ret = task->thread.gcr_user_incl << PR_MTE_TAG_SHIFT;
+	ret = incl << PR_MTE_TAG_SHIFT;
 
 	switch (task->thread.sctlr_tcf0) {
 	case SCTLR_EL1_TCF0_NONE: