ARM: 9430/1: entry: Do a dummy read from VMAP shadow

BugLink: https://bugs.launchpad.net/bugs/2101915

commit 44e9a3bb76e5f2eecd374c8176b2c5163c8bb2e2 upstream.

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.

Cc: stable@vger.kernel.org
Fixes: a1c510d0ad ("ARM: implement support for vmap'ed stacks")
Link: https://lore.kernel.org/linux-arm-kernel/a1a1d062-f3a2-4d05-9836-3b098de9db6d@foss.st.com/
Reported-by: Clement LE GOFFIC <clement.legoffic@foss.st.com>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

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>
@@ -555,6 +556,13 @@ ENTRY(__switch_to)
 	@ entries covering the vmalloc region.
 	@
 	ldr	r2, [ip]
+#ifdef CONFIG_KASAN_VMALLOC
+	@ 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, r2, ip, lsr #KASAN_SHADOW_SCALE_SHIFT
+	ldr	r2, [r2]
+#endif
 #endif
 
 	@ When CONFIG_THREAD_INFO_IN_TASK=n, the update of SP itself is what