linux-kernel - [PATCH 2/2] kasan: Update required compiler versions in documentation

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Message-Id: <20200629104157.3242503-2-elver@google.com>
Date:   Mon, 29 Jun 2020 12:41:57 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, akpm@...ux-foundation.org
Cc:     dvyukov@...gle.com, glider@...gle.com, andreyknvl@...gle.com,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        aryabinin@...tuozzo.com, ndesaulniers@...gle.com,
        walter-zh.wu@...iatek.com, arnd@...db.de, dja@...ens.net,
        linux-doc@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH 2/2] kasan: Update required compiler versions in documentation

Updates the recently changed compiler requirements for KASAN. In
particular, we require GCC >= 8.3.0, and add a note that Clang 11
supports OOB detection of globals.

Fixes: 7b861a53e46b ("kasan: Bump required compiler version")
Fixes: acf7b0bf7dcf ("kasan: Fix required compiler version")
Signed-off-by: Marco Elver <elver@...gle.com>
---
 Documentation/dev-tools/kasan.rst |  7 ++-----
 lib/Kconfig.kasan                 | 24 +++++++++++++++---------
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index c652d740735d..15a2a53e77b0 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -13,11 +13,8 @@ KASAN uses compile-time instrumentation to insert validity checks before every
 memory access, and therefore requires a compiler version that supports that.
 
 Generic KASAN is supported in both GCC and Clang. With GCC it requires version
-4.9.2 or later for basic support and version 5.0 or later for detection of
-out-of-bounds accesses for stack and global variables and for inline
-instrumentation mode (see the Usage section). With Clang it requires version
-7.0.0 or later and it doesn't support detection of out-of-bounds accesses for
-global variables yet.
+8.3.0 or later. With Clang it requires version 7.0.0 or later, but detection of
+out-of-bounds accesses for global variables is only supported since Clang 11.
 
 Tag-based KASAN is only supported in Clang and requires version 7.0.0 or later.
 
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index 89053defc0d9..047b53dbfd58 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -40,6 +40,7 @@ choice
 	  software tag-based KASAN (a version based on software memory
 	  tagging, arm64 only, similar to userspace HWASan, enabled with
 	  CONFIG_KASAN_SW_TAGS).
+
 	  Both generic and tag-based KASAN are strictly debugging features.
 
 config KASAN_GENERIC
@@ -51,16 +52,18 @@ config KASAN_GENERIC
 	select STACKDEPOT
 	help
 	  Enables generic KASAN mode.
-	  Supported in both GCC and Clang. With GCC it requires version 4.9.2
-	  or later for basic support and version 5.0 or later for detection of
-	  out-of-bounds accesses for stack and global variables and for inline
-	  instrumentation mode (CONFIG_KASAN_INLINE). With Clang it requires
-	  version 3.7.0 or later and it doesn't support detection of
-	  out-of-bounds accesses for global variables yet.
+
+	  This mode is supported in both GCC and Clang. With GCC it requires
+	  version 8.3.0 or later. With Clang it requires version 7.0.0 or
+	  later, but detection of out-of-bounds accesses for global variables
+	  is supported only since Clang 11.
+
 	  This mode consumes about 1/8th of available memory at kernel start
 	  and introduces an overhead of ~x1.5 for the rest of the allocations.
 	  The performance slowdown is ~x3.
+
 	  For better error detection enable CONFIG_STACKTRACE.
+
 	  Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
 	  (the resulting kernel does not boot).
 
@@ -73,15 +76,19 @@ config KASAN_SW_TAGS
 	select STACKDEPOT
 	help
 	  Enables software tag-based KASAN mode.
+
 	  This mode requires Top Byte Ignore support by the CPU and therefore
-	  is only supported for arm64.
-	  This mode requires Clang version 7.0.0 or later.
+	  is only supported for arm64. This mode requires Clang version 7.0.0
+	  or later.
+
 	  This mode consumes about 1/16th of available memory at kernel start
 	  and introduces an overhead of ~20% for the rest of the allocations.
 	  This mode may potentially introduce problems relating to pointer
 	  casting and comparison, as it embeds tags into the top byte of each
 	  pointer.
+
 	  For better error detection enable CONFIG_STACKTRACE.
+
 	  Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
 	  (the resulting kernel does not boot).
 
@@ -107,7 +114,6 @@ config KASAN_INLINE
 	  memory accesses. This is faster than outline (in some workloads
 	  it gives about x2 boost over outline instrumentation), but
 	  make kernel's .text size much bigger.
-	  For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later.
 
 endchoice
 
-- 
2.27.0.212.ge8ba1cc988-goog