[PATCH] ARM: entry: Do a dummy read from VMAP shadow

[Linus Walleij]

When switching task, in addition to a dummy read from the new
VMAP stack, also do a dummy read from the VMAP stack's
corresponding KASAN shadow memory to sync things up in
the new MM context.

Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
---
 arch/arm/kernel/entry-armv.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 1dfae1af8e31..ed2d0d89e2e9 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -25,6 +25,7 @@
 #include <asm/tls.h>
 #include <asm/system_info.h>
 #include <asm/uaccess-asm.h>
+#include <asm/kasan_def.h>

 #include "entry-header.S"
 #include <asm/probes.h>
@@ -561,6 +562,13 @@ ENTRY(__switch_to)
     @ entries covering the vmalloc region.
     @
     ldr    r2, [ip]
+#ifdef CONFIG_KASAN
+    @ Also dummy read from the KASAN shadow memory for the new stack if we
+    @ are using KASAN
+    mov_l    r2, KASAN_SHADOW_OFFSET
+    add    r2, ip, lsr #KASAN_SHADOW_SCALE_SHIFT
+    ldr    r2, [r2]
+#endif
 #endif

     @ When CONFIG_THREAD_INFO_IN_TASK=3Dn, the update of SP itself is what
--=20
2.46.2

We still get crashes in do_translation_fault() so we need the more
thorough solution. Maybe this is needed too.

Yours,
Linus Walleij