Move CFLAGS_KASAN*, CFLAGS_UBSAN, CFLAGS_KCSAN to Makefile.kasan,
Makefile.ubsan, Makefile.kcsan, respectively.

This commit also avoids the same -fsanitize=* flags being added to
CFLAGS_UBSAN multiple times.

Prior to this commit, the ubsan flags were appended by the '+='
operator, without any initialization. Some build targets such as
'make bindeb-pkg' recurses to the top Makefile, and ended up with
adding the same flags to CFLAGS_UBSAN twice.

Clear CFLAGS_UBSAN with ':=' to make it a simply expanded variable.
This is better than a recursively expanded variable, which evaluates
$(call cc-option, ...) multiple times before Kbuild starts descending
to subdirectories.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Marco Elver <elver@google.com>

Add support for compounded read-write instrumentation if supported by
the compiler. Adds the necessary instrumentation functions, and a new
type which is used to generate a more descriptive report.

Furthermore, such compounded memory access instrumentation is excluded
from the "assume aligned writes up to word size are atomic" rule,
because we cannot assume that the compiler emits code that is atomic for
compound ops.

LLVM/Clang added support for the feature in:
https://github.com/llvm/llvm-project/commit/785d41a261d136b64ab6c15c5d35f2adc5ad53e3



The new instrumentation is emitted for sets of memory accesses in the
same basic block to the same address with at least one read appearing
before a write. These typically result from compound operations such as
++, --, +=, -=, |=, &=, etc. but also equivalent forms such as "var =
var + 1". Where the compiler determines that it is equivalent to emit a
call to a single __tsan_read_write instead of separate __tsan_read and
__tsan_write, we can then benefit from improved performance and better
reporting for such access patterns.

The new reports now show that the ops are both reads and writes, for
example:

	read-write to 0xffffffff90548a38 of 8 bytes by task 143 on cpu 3:
	 test_kernel_rmw_array+0x45/0xa0
	 access_thread+0x71/0xb0
	 kthread+0x21e/0x240
	 ret_from_fork+0x22/0x30

	read-write to 0xffffffff90548a38 of 8 bytes by task 144 on cpu 2:
	 test_kernel_rmw_array+0x45/0xa0
	 access_thread+0x71/0xb0
	 kthread+0x21e/0x240
	 ret_from_fork+0x22/0x30

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Currently, the top Makefile includes all of scripts/Makefile.<feature>
even if the associated CONFIG option is disabled.

Do not include unneeded Makefiles in order to slightly optimize the
parse stage.

Include $(include-y), and ignore $(include-).

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

GCC version 11 recently implemented all requirements to correctly
support KCSAN:

1. Correct no_sanitize-attribute inlining behaviour:
   https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=4089df8ef4a63126b0774c39b6638845244c20d2

2. --param=tsan-distinguish-volatile
   https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=ab2789ec507a94f1a75a6534bca51c7b39037ce0

3. --param=tsan-instrument-func-entry-exit
   https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=06712fc68dc9843d9af7c7ac10047f49d305ad76



Therefore, we can re-enable GCC for KCSAN, and document the new compiler
requirements.

Signed-off-by: Marco Elver <elver@google.com>
Cc: Martin Liska <mliska@suse.cz>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Clang (unlike GCC) removes reads before writes with matching addresses
in the same basic block. This is an optimization for TSAN, since writes
will always cause conflict if the preceding read would have.

However, for KCSAN we cannot rely on this option, because we apply
several special rules to writes, in particular when the
KCSAN_ASSUME_PLAIN_WRITES_ATOMIC option is selected. To avoid missing
potential data races, pass the -tsan-instrument-read-before-write option
to Clang if it is available [1].

[1] https://github.com/llvm/llvm-project/commit/151ed6aa38a3ec6c01973b35f684586b6e1c0f7e



Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20200521142047.169334-5-elver@google.com

In the kernel, the "volatile" keyword is used in various concurrent
contexts, whether in low-level synchronization primitives or for
legacy reasons. If supported by the compiler, it will be assumed
that aligned volatile accesses up to sizeof(long long) (matching
compiletime_assert_rwonce_type()) are atomic.

Recent versions of Clang [1] (GCC tentative [2]) can instrument
volatile accesses differently. Add the option (required) to enable the
instrumentation, and provide the necessary runtime functions. None of
the updated compilers are widely available yet (Clang 11 will be the
first release to support the feature).

[1] https://github.com/llvm/llvm-project/commit/5a2c31116f412c3b6888be361137efd705e05814
[2] https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544452.html



This change allows removing of any explicit checks in primitives such as
READ_ONCE() and WRITE_ONCE().

 [ bp: Massage commit message a bit. ]

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200521142047.169334-4-elver@google.com

To avoid inserting  __tsan_func_{entry,exit}, add option if supported by
compiler. Currently only Clang can be told to not emit calls to these
functions. It is safe to not emit these, since KCSAN does not rely on
them.

Note that, if we disable __tsan_func_{entry,exit}(), we need to disable
tail-call optimization in sanitized compilation units, as otherwise we
may skip frames in the stack trace; in particular when the tail called
function is one of the KCSAN's runtime functions, and a report is
generated, we might miss the function where the actual access occurred.

Since __tsan_func_{entry,exit}() insertion effectively disabled
tail-call optimization, there should be no observable change.

This was caught and confirmed with kcsan-test & UNWINDER_ORC.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200521142047.169334-3-elver@google.com

Kernel Concurrency Sanitizer (KCSAN) is a dynamic data-race detector for
kernel space. KCSAN is a sampling watchpoint-based data-race detector.
See the included Documentation/dev-tools/kcsan.rst for more details.

This patch adds basic infrastructure, but does not yet enable KCSAN for
any architecture.

Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>