[PATCH 1/2] kasan: arm64: set TCR_EL1.TBID1 when enabled

[Peter Collingbourne]

On hardware supporting pointer authentication, we previously ended up
enabling TBI on instruction accesses when tag-based ASAN was enabled,
but this was costing us 8 bits of PAC entropy, which was unnecessary
since tag-based ASAN does not require TBI on instruction accesses. Get
them back by setting TCR_EL1.TBID1.

Signed-off-by: Peter Collingbourne <pcc at google.com>
Link: https://linux-review.googlesource.com/id/I3dded7824be2e70ea64df0aabab9598d5aebfcc4
---
 arch/arm64/include/asm/pgtable-hwdef.h | 1 +
 arch/arm64/mm/proc.S                   | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
index 01a96d07ae74..42442a0ae2ab 100644
--- a/arch/arm64/include/asm/pgtable-hwdef.h
+++ b/arch/arm64/include/asm/pgtable-hwdef.h
@@ -260,6 +260,7 @@
 #define TCR_TBI1		(UL(1) << 38)
 #define TCR_HA			(UL(1) << 39)
 #define TCR_HD			(UL(1) << 40)
+#define TCR_TBID1		(UL(1) << 52)
 #define TCR_NFD0		(UL(1) << 53)
 #define TCR_NFD1		(UL(1) << 54)
 #define TCR_E0PD0		(UL(1) << 55)
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 23c326a06b2d..97a97a61a8dc 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -40,7 +40,7 @@
 #define TCR_CACHE_FLAGS	TCR_IRGN_WBWA | TCR_ORGN_WBWA
 
 #ifdef CONFIG_KASAN_SW_TAGS
-#define TCR_KASAN_FLAGS TCR_TBI1
+#define TCR_KASAN_FLAGS TCR_TBI1 | TCR_TBID1
 #else
 #define TCR_KASAN_FLAGS 0
 #endif
-- 
2.29.2.454.gaff20da3a2-goog