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

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Message-Id: <26fb6165a17abcf61222eda5184c030fb6b133d1.1596544734.git.andreyknvl@google.com>
Date:   Tue,  4 Aug 2020 14:41:26 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Walter Wu <walter-zh.wu@...iatek.com>,
        Elena Petrova <lenaptr@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v2 3/5] kasan, arm64: don't instrument functions that enable kasan

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@...gle.com>
---
 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)
 	rest_init();
 }
 
-asmlinkage __visible void __init start_kernel(void)
+asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
 {
 	char *command_line;
 	char *after_dashes;
-- 
2.28.0.163.g6104cc2f0b6-goog