Re: [PATCH] kasan: Remove use after scope bugs detection.

On Fri, Jan 11, 2019 at 09:58:42PM +0300, Andrey Ryabinin wrote:

Use after scope bugs detector seems to be almost entirely useless
for the linux kernel. It exists over two years, but I've seen only
one valid bug so far [1]. And the bug was fixed before it has been
reported. There were some other use-after-scope reports, but they
were false-positives due to different reasons like incompatibility
with structleak plugin.

This feature significantly increases stack usage, especially with
GCC < 9 version, and causes a 32K stack overflow. It probably
adds performance penalty too.

Given all that, let's remove use-after-scope detector entirely.

While preparing this patch I've noticed that we mistakenly enable
use-after-scope detection for clang compiler regardless of
CONFIG_KASAN_EXTRA setting. This is also fixed now.

[1] http://lkml.kernel.org/r/[off-list ref]

Signed-off-by: Andrey Ryabinin <redacted>
Cc: Qian Cai <redacted>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <redacted>
---
 arch/arm64/include/asm/memory.h |  4 ----
 lib/Kconfig.debug               |  1 -
 lib/Kconfig.kasan               | 10 ----------
 lib/test_kasan.c                | 24 ------------------------
 mm/kasan/generic.c              | 19 -------------------
 mm/kasan/generic_report.c       |  3 ---
 mm/kasan/kasan.h                |  3 ---
 scripts/Makefile.kasan          |  5 -----
 scripts/gcc-plugins/Kconfig     |  4 ----
 9 files changed, 73 deletions(-)

For the arm64 part:

Acked-by: Will Deacon <redacted>

but I defer to you and Dmitry as to whether or not you go ahead with this.

Will

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