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diff --git a/sys/arm64/arm64/pmap.c b/sys/arm64/arm64/pmap.c
--- a/sys/arm64/arm64/pmap.c
+++ b/sys/arm64/arm64/pmap.c
@@ -1647,8 +1647,11 @@
* Walks the page tables to translate a kernel virtual address to a
* physical address. Returns true if the kva is valid and stores the
* physical address in pa if it is not NULL.
+ *
+ * See the comment above data_abort() for the rationale for specifying
+ * NO_PERTHREAD_SSP here.
*/
-bool
+bool NO_PERTHREAD_SSP
pmap_klookup(vm_offset_t va, vm_paddr_t *pa)
{
pt_entry_t *pte, tpte;
@@ -7052,10 +7055,6 @@
/* Store the new curthread */
PCPU_SET(curthread, new);
-#if defined(PERTHREAD_SSP)
- /* Set the new threads SSP canary */
- __asm("msr sp_el0, %0" :: "r"(&new->td_md.md_canary));
-#endif
/* And the new pcb */
pcb = new->td_pcb;
diff --git a/sys/arm64/arm64/swtch.S b/sys/arm64/arm64/swtch.S
--- a/sys/arm64/arm64/swtch.S
+++ b/sys/arm64/arm64/swtch.S
@@ -80,9 +80,17 @@
/* This returns the thread pointer so no need to save it */
bl ptrauth_switch
+#ifdef PERTHREAD_SSP
+ mov x19, x0
+#endif
/* This returns the thread pcb */
bl pmap_switch
mov x4, x0
+#ifdef PERTHREAD_SSP
+ /* Update the per-thread stack canary pointer. */
+ add x19, x19, #(TD_MD_CANARY)
+ msr sp_el0, x19
+#endif
/* If we are single stepping, enable it */
ldr w5, [x4, #PCB_FLAGS]
@@ -159,6 +167,11 @@
mov x2, x21
mov x1, x20
mov x0, x19
+#ifdef PERTHREAD_SSP
+ /* Update the per-thread stack canary pointer. */
+ add x20, x20, #(TD_MD_CANARY)
+ msr sp_el0, x20
+#endif
/*
* Release the old thread.
diff --git a/sys/arm64/arm64/trap.c b/sys/arm64/arm64/trap.c
--- a/sys/arm64/arm64/trap.c
+++ b/sys/arm64/arm64/trap.c
@@ -241,7 +241,13 @@
panic("Unhandled EL%d external data abort", lower ? 0: 1);
}
-static void
+/*
+ * It is unsafe to access the stack canary value stored in "td" until
+ * kernel map translation faults are handled, see the pmap_klookup() call below.
+ * Thus, stack-smashing detection with per-thread canaries must be disabled in
+ * this function.
+ */
+static void NO_PERTHREAD_SSP
data_abort(struct thread *td, struct trapframe *frame, uint64_t esr,
uint64_t far, int lower)
{
@@ -449,7 +455,10 @@
}
#endif
-void
+/*
+ * See the comment above data_abort().
+ */
+void NO_PERTHREAD_SSP
do_el1h_sync(struct thread *td, struct trapframe *frame)
{
uint32_t exception;
diff --git a/sys/arm64/include/param.h b/sys/arm64/include/param.h
--- a/sys/arm64/include/param.h
+++ b/sys/arm64/include/param.h
@@ -105,6 +105,12 @@
#define KSTACK_GUARD_PAGES 1 /* pages of kstack guard; 0 disables */
#define PCPU_PAGES 1
+#ifdef PERTHREAD_SSP
+#define NO_PERTHREAD_SSP __nostackprotector
+#else
+#define NO_PERTHREAD_SSP
+#endif
+
/*
* Mach derived conversion macros
*/
diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -896,6 +896,16 @@
#define __nosanitizethread
#endif
+/*
+ * Make it possible to opt out of stack smashing protection.
+ */
+#if __has_attribute(no_stack_protector)
+#define __nostackprotector __attribute__((no_stack_protector))
+#else
+#define __nostackprotector \
+ __attribute__((__optimize__("-fno-stack-protector")))
+#endif
+
/* Guard variables and structure members by lock. */
#define __guarded_by(x) __lock_annotate(guarded_by(x))
#define __pt_guarded_by(x) __lock_annotate(pt_guarded_by(x))

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