[PATCH v2 3/5] kasan, arm64: don't instrument functions that enable kasan

From: Andrey Konovalov
Date: Tue Aug 04 2020 - 08:42:40 EST

This patch prepares Software Tag-Based KASAN for stack tagging support.

With stack tagging enabled, KASAN tags stack variable in each function
in its prologue. In start_kernel() stack variables get tagged before KASAN
is enabled via setup_arch()->kasan_init(). As the result the tags for
start_kernel()'s stack variables end up in the temporary shadow memory.
Later when KASAN gets enabled, switched to normal shadow, and starts
checking tags, this leads to false-positive reports, as proper tags are
missing in normal shadow.

Disable KASAN instrumentation for start_kernel(). Also disable it for
arm64's setup_arch() as a precaution (it doesn't have any stack variables
right now).

Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
arch/arm64/kernel/setup.c | 2 +-
init/main.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 93b3844cf442..575da075a2b9 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -276,7 +276,7 @@ arch_initcall(reserve_memblock_reserved_regions);

u64 __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1] = INVALID_HWID };

-void __init setup_arch(char **cmdline_p)
+void __init __no_sanitize_address setup_arch(char **cmdline_p)
init_mm.start_code = (unsigned long) _text;
init_mm.end_code = (unsigned long) _etext;
diff --git a/init/main.c b/init/main.c
index 0ead83e86b5a..7e5e25d9fe42 100644
--- a/init/main.c
+++ b/init/main.c
@@ -827,7 +827,7 @@ void __init __weak arch_call_rest_init(void)

-asmlinkage __visible void __init start_kernel(void)
+asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
char *command_line;
char *after_dashes;