[PATCH 2/2] arm64: suspend: Save GCS state over suspend

[Mark Brown]

GCSCRE0_EL1 and GCSPR_EL0 are live registers for EL0 on systems with GCS
but are not saved and restored by cpu_do_suspend()/cpu_do_resume(). This
means that the task that initiated suspend can return to userspace with
UNKNOWN or incorrect values for GCSPR_EL0 and GCSCRE0_EL1 (many fields
in GCSCRE0_EL1 reset to 0).  This will in turn lead to ongoing
corruption, including not restoring mode until a task with a different
GCS mode is run.  Fix this by saving and restoring the values over
suspend.

This increases the size of struct cpu_suspend_ctx by 16 bytes.

Fixes: 5d8b172e7005 ("arm64: Add Kconfig for Guarded Control Stack (GCS)")
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 arch/arm64/include/asm/suspend.h |  2 +-
 arch/arm64/mm/proc.S             | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/suspend.h b/arch/arm64/include/asm/suspend.h
index eb9ce315f146..8e9c97aab15a 100644
--- a/arch/arm64/include/asm/suspend.h
+++ b/arch/arm64/include/asm/suspend.h
@@ -2,7 +2,7 @@
 #ifndef __ASM_SUSPEND_H
 #define __ASM_SUSPEND_H
 
-#define NR_CTX_REGS 16
+#define NR_CTX_REGS 18
 #define NR_CALLEE_SAVED_REGS 12
 
 /*
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 664ea9e3b9ad..99aacf03367d 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -121,6 +121,12 @@ alternative_else_nop_endif
 alternative_if ARM64_HAS_S1POE
 	mrs	x2, REG_POR_EL0
 	str	x2, [x0, #120]
+alternative_else_nop_endif
+alternative_if ARM64_HAS_GCS
+	mrs	x2, REG_GCSPR_EL0
+	str	x2, [x0, #128]
+	mrs	x2, REG_GCSCRE0_EL1
+	str	x2, [x0, #136]
 alternative_else_nop_endif
 	ret
 SYM_FUNC_END(cpu_do_suspend)
@@ -168,6 +174,12 @@ alternative_if ARM64_HAS_S1POE
 	ldr	x2, [x0, #120]
 	msr	REG_POR_EL0, x2
 alternative_else_nop_endif
+alternative_if ARM64_HAS_GCS
+	ldr	x2, [x0, #128]
+	msr	REG_GCSPR_EL0, x2
+	ldr	x2, [x0, #136]
+	msr	REG_GCSCRE0_EL1, x2
+alternative_else_nop_endif
 
 	msr	sctlr_el1, x12
 	set_this_cpu_offset x13

-- 
2.47.3