I realize that we fairly recently raised it to 4.8, but the fact is, 4.9
is a much better minimum version to target.
We have a number of workarounds for actual bugs in pre-4.9 gcc versions
(including things like internal compiler errors on ARM), but we also
have some syntactic workarounds for lacking features.
In particular, raising the minimum to 4.9 means that we can now just
assume _Generic() exists, which is likely the much better replacement
for a lot of very convoluted built-time magic with conditionals on
sizeof and/or __builtin_choose_expr() with same_type() etc.
Using _Generic also means that you will need to have a very recent
version of 'sparse', but thats easy to build yourself, and much less of
a hassle than some old gcc version can be.
The latest (in a long string) of reasons for minimum compiler version
upgrades was commit 5435f73d5c ("efi/x86: Fix build with gcc 4").
Ard points out that RHEL 7 uses gcc-4.8, but the people who stay back on
old RHEL versions persumably also don't build their own kernels anyway.
And maybe they should cross-built or just have a little side affair with
a newer compiler?
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Merge the state of the locking kcsan branch before the read/write_once()
and the atomics modifications got merged.
Squash the fallout of the rebase on top of the read/write once and atomic
fallback work into the merge. The history of the original branch is
preserved in tag locking-kcsan-2020-06-02.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
It is very rare to see versions of GCC prior to 4.8 being used to build
the mainline kernel. These old compilers are also know to have codegen
issues which can lead to silent miscompilation:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145
Raise the minimum GCC version for kernel build to 4.8 and remove some
tautological Kconfig dependencies as a consequence.
Cc: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Since the use of -fsanitize=thread is an implementation detail of KCSAN,
the name __no_sanitize_thread could be misleading if used widely.
Instead, we introduce the __no_kcsan attribute which is shorter and more
accurate in the context of KCSAN.
This matches the attribute name __no_kcsan_or_inline. The use of
__kcsan_or_inline itself is still required for __always_inline functions
to retain compatibility with older compilers.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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>
On x86-64, with CONFIG_RETPOLINE=n, GCC's "global common subexpression
elimination" optimization results in ___bpf_prog_run()'s jumptable code
changing from this:
select_insn:
jmp *jumptable(, %rax, 8)
...
ALU64_ADD_X:
...
jmp *jumptable(, %rax, 8)
ALU_ADD_X:
...
jmp *jumptable(, %rax, 8)
to this:
select_insn:
mov jumptable, %r12
jmp *(%r12, %rax, 8)
...
ALU64_ADD_X:
...
jmp *(%r12, %rax, 8)
ALU_ADD_X:
...
jmp *(%r12, %rax, 8)
The jumptable address is placed in a register once, at the beginning of
the function. The function execution can then go through multiple
indirect jumps which rely on that same register value. This has a few
issues:
1) Objtool isn't smart enough to be able to track such a register value
across multiple recursive indirect jumps through the jump table.
2) With CONFIG_RETPOLINE enabled, this optimization actually results in
a small slowdown. I measured a ~4.7% slowdown in the test_bpf
"tcpdump port 22" selftest.
This slowdown is actually predicted by the GCC manual:
Note: When compiling a program using computed gotos, a GCC
extension, you may get better run-time performance if you
disable the global common subexpression elimination pass by
adding -fno-gcse to the command line.
So just disable the optimization for this function.
Fixes: e55a73251d ("bpf: Fix ORC unwinding in non-JIT BPF code")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/30c3ca29ba037afcbd860a8672eef0021addf9fe.1563413318.git.jpoimboe@redhat.com
Pull misc clang fixes from Miguel Ojeda:
- A fix for OPTIMIZER_HIDE_VAR from Michael S Tsirkin
- Update clang-format with the latest for_each macro list from Jason
Gunthorpe
* tag 'compiler-attributes-for-linus-v5.0-rc3' of git://github.com/ojeda/linux:
include/linux/compiler*.h: fix OPTIMIZER_HIDE_VAR
* tag 'clang-format-for-linus-v5.0-rc3' of git://github.com/ojeda/linux:
clang-format: Update .clang-format with the latest for_each macro list
Since commit 815f0ddb34 ("include/linux/compiler*.h: make compiler-*.h
mutually exclusive") clang no longer reuses the OPTIMIZER_HIDE_VAR macro
from compiler-gcc - instead it gets the version in
include/linux/compiler.h. Unfortunately that version doesn't actually
prevent compiler from optimizing out the variable.
Fix up by moving the macro out from compiler-gcc.h to compiler.h.
Compilers without incline asm support will keep working
since it's protected by an ifdef.
Also fix up comments to match reality since we are no longer overriding
any macros.
Build-tested with gcc and clang.
Fixes: 815f0ddb34 ("include/linux/compiler*.h: make compiler-*.h mutually exclusive")
Cc: Eli Friedman <efriedma@codeaurora.org>
Cc: Joe Perches <joe@perches.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
This commit splits the current CONFIG_KASAN config option into two:
1. CONFIG_KASAN_GENERIC, that enables the generic KASAN mode (the one
that exists now);
2. CONFIG_KASAN_SW_TAGS, that enables the software tag-based KASAN mode.
The name CONFIG_KASAN_SW_TAGS is chosen as in the future we will have
another hardware tag-based KASAN mode, that will rely on hardware memory
tagging support in arm64.
With CONFIG_KASAN_SW_TAGS enabled, compiler options are changed to
instrument kernel files with -fsantize=kernel-hwaddress (except the ones
for which KASAN_SANITIZE := n is set).
Both CONFIG_KASAN_GENERIC and CONFIG_KASAN_SW_TAGS support both
CONFIG_KASAN_INLINE and CONFIG_KASAN_OUTLINE instrumentation modes.
This commit also adds empty placeholder (for now) implementation of
tag-based KASAN specific hooks inserted by the compiler and adjusts
common hooks implementation.
While this commit adds the CONFIG_KASAN_SW_TAGS config option, this option
is not selectable, as it depends on HAVE_ARCH_KASAN_SW_TAGS, which we will
enable once all the infrastracture code has been added.
Link: http://lkml.kernel.org/r/b2550106eb8a68b10fefbabce820910b115aa853.1544099024.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The __no_sanitize_address_or_inline and __no_kasan_or_inline defines
are almost identical. The only difference is that __no_kasan_or_inline
does not have the 'notrace' attribute.
To be able to replace __no_sanitize_address_or_inline with the older
definition, add 'notrace' to __no_kasan_or_inline and change to two
users of __no_sanitize_address_or_inline in the s390 code.
The 'notrace' option is necessary for e.g. the __load_psw_mask function
in arch/s390/include/asm/processor.h. Without the option it is possible
to trace __load_psw_mask which leads to kernel stack overflow.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Pointed-out-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull compiler attribute updates from Miguel Ojeda:
"This is an effort to disentangle the include/linux/compiler*.h headers
and bring them up to date.
The main idea behind the series is to use feature checking macros
(i.e. __has_attribute) instead of compiler version checks (e.g.
GCC_VERSION), which are compiler-agnostic (so they can be shared,
reducing the size of compiler-specific headers) and version-agnostic.
Other related improvements have been performed in the headers as well,
which on top of the use of __has_attribute it has amounted to a
significant simplification of these headers (e.g. GCC_VERSION is now
only guarding a few non-attribute macros).
This series should also help the efforts to support compiling the
kernel with clang and icc. A fair amount of documentation and comments
have also been added, clarified or removed; and the headers are now
more readable, which should help kernel developers in general.
The series was triggered due to the move to gcc >= 4.6. In turn, this
series has also triggered Sparse to gain the ability to recognize
__has_attribute on its own.
Finally, the __nonstring variable attribute series has been also
applied on top; plus two related patches from Nick Desaulniers for
unreachable() that came a bit afterwards"
* tag 'compiler-attributes-for-linus-4.20-rc1' of https://github.com/ojeda/linux:
compiler-gcc: remove comment about gcc 4.5 from unreachable()
compiler.h: update definition of unreachable()
Compiler Attributes: ext4: remove local __nonstring definition
Compiler Attributes: auxdisplay: panel: use __nonstring
Compiler Attributes: enable -Wstringop-truncation on W=1 (gcc >= 8)
Compiler Attributes: add support for __nonstring (gcc >= 8)
Compiler Attributes: add MAINTAINERS entry
Compiler Attributes: add Doc/process/programming-language.rst
Compiler Attributes: remove uses of __attribute__ from compiler.h
Compiler Attributes: KENTRY used twice the "used" attribute
Compiler Attributes: use feature checks instead of version checks
Compiler Attributes: add missing SPDX ID in compiler_types.h
Compiler Attributes: remove unneeded sparse (__CHECKER__) tests
Compiler Attributes: homogenize __must_be_array
Compiler Attributes: remove unneeded tests
Compiler Attributes: always use the extra-underscores syntax
Compiler Attributes: remove unused attributes
Pull s390 updates from Martin Schwidefsky:
- Improved access control for the zcrypt driver, multiple device nodes
can now be created with different access control lists
- Extend the pkey API to provide random protected keys, this is useful
for encrypted swap device with ephemeral protected keys
- Add support for virtually mapped kernel stacks
- Rework the early boot code, this moves the memory detection into the
boot code that runs prior to decompression.
- Add KASAN support
- Bug fixes and cleanups
* tag 's390-4.20-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux: (83 commits)
s390/pkey: move pckmo subfunction available checks away from module init
s390/kasan: support preemptible kernel build
s390/pkey: Load pkey kernel module automatically
s390/perf: Return error when debug_register fails
s390/sthyi: Fix machine name validity indication
s390/zcrypt: fix broken zcrypt_send_cprb in-kernel api function
s390/vmalloc: fix VMALLOC_START calculation
s390/mem_detect: add missing include
s390/dumpstack: print psw mask and address again
s390/crypto: Enhance paes cipher to accept variable length key material
s390/pkey: Introduce new API for transforming key blobs
s390/pkey: Introduce new API for random protected key verification
s390/pkey: Add sysfs attributes to emit secure key blobs
s390/pkey: Add sysfs attributes to emit protected key blobs
s390/pkey: Define protected key blob format
s390/pkey: Introduce new API for random protected key generation
s390/zcrypt: add ap_adapter_mask sysfs attribute
s390/zcrypt: provide apfs failure code on type 86 error reply
s390/zcrypt: zcrypt device driver cleanup
s390/kasan: add support for mem= kernel parameter
...
Remove the comment about being unable to detect __builtin_unreachable.
__builtin_unreachable was implemented in the GCC 4.5 timeframe. The
kernel's minimum supported version of GCC is 4.6 since commit
cafa0010cd ("Raise the minimum required gcc version to 4.6"). Commit
cb984d101b ("compiler-gcc: integrate the various compiler-gcc[345].h
files") shows that unreachable() had different guards based on GCC
version.
Suggested-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Due to conflict between kasan instrumentation and inlining
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368 functions which are
defined as inline could not be called from functions defined with
__no_sanitize_address.
Introduce __no_sanitize_address_or_inline which would expand to
__no_sanitize_address when the kernel is built with kasan support and
to inline otherwise. This helps to avoid disabling kasan
instrumentation for entire files.
Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Instead of using version checks per-compiler to define (or not)
each attribute, use __has_attribute to test for them, following
the cleanup started with commit 815f0ddb34
("include/linux/compiler*.h: make compiler-*.h mutually exclusive"),
which is supported on gcc >= 5, clang >= 2.9 and icc >= 17.
In the meantime, to support 4.6 <= gcc < 5, we implement
__has_attribute by hand.
All the attributes that can be unconditionally defined and directly
map to compiler attribute(s) (even if optional) have been moved
to a new file include/linux/compiler_attributes.h
In an effort to make the file as regular as possible, comments
stating the purpose of attributes have been removed. Instead,
links to the compiler docs have been added (i.e. to gcc and,
if available, to clang as well). In addition, they have been sorted.
Finally, if an attribute is optional (i.e. if it is guarded
by __has_attribute), the reason has been stated for future reference.
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Sparse knows about a few more attributes now, so we can remove
the __CHECKER__ conditions from them (which, in turn, allow us
to move some of them later on to compiler_attributes.h).
* assume_aligned: since sparse's commit ffc860b ("sparse:
ignore __assume_aligned__ attribute"), included in 0.5.1
* error: since sparse's commit 0a04210 ("sparse: Add 'error'
to ignored attributes"), included in 0.5.0
* hotpatch: since sparse's commit 6043210 ("sparse/parse.c:
ignore hotpatch attribute"), included in 0.5.1
* warning: since sparse's commit 977365d ("Avoid "attribute
'warning': unknown attribute" warning"), included in 0.4.2
On top of that, __must_be_array does not need it either because:
* Even ancient versions of sparse do not have a problem
* BUILD_BUG_ON_ZERO() is currently disabled for __CHECKER__
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Different definitions of __must_be_array:
* gcc: disabled for __CHECKER__
* clang: same definition as gcc's, but without __CHECKER__
* intel: the comment claims __builtin_types_compatible_p()
is unsupported; but icc seems to support it since 13.0.1
(released in 2012). See https://godbolt.org/z/S0l6QQ
Therefore, we can remove all of them and have a single definition
in compiler.h
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
The attribute syntax optionally allows to surround attribute names
with "__" in order to avoid collisions with macros of the same name
(see https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html).
This homogenizes all attributes to use the syntax with underscores.
While there are currently only a handful of cases of some TUs defining
macros like "error" which may collide with the attributes,
this should prevent futures surprises.
This has been done only for "standard" attributes supported by
the major compilers. In other words, those of third-party tools
(e.g. sparse, plugins...) have not been changed for the moment.
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
