linux-stable.git/include/linux/compiler_types.h, branch v5.13.4

kcov: add __no_sanitize_coverage to fix noinstr for all architectures

2021-07-20T14:00:22+00:00

[ Upstream commit 540540d06e9d9b3769b46d88def90f7e7c002322 ]

Until now no compiler supported an attribute to disable coverage
instrumentation as used by KCOV.

To work around this limitation on x86, noinstr functions have their
coverage instrumentation turned into nops by objtool.  However, this
solution doesn't scale automatically to other architectures, such as
arm64, which are migrating to use the generic entry code.

Clang [1] and GCC [2] have added support for the attribute recently.
[1] https://github.com/llvm/llvm-project/commit/280333021e9550d80f5c1152a34e33e81df1e178
[2] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=cec4d4a6782c9bd8d071839c50a239c49caca689
The changes will appear in Clang 13 and GCC 12.

Add __no_sanitize_coverage for both compilers, and add it to noinstr.

Note: In the Clang case, __has_feature(coverage_sanitizer) is only true if
the feature is enabled, and therefore we do not require an additional
defined(CONFIG_KCOV) (like in the GCC case where __has_attribute(..) is
always true) to avoid adding redundant attributes to functions if KCOV is
off.  That being said, compilers that support the attribute will not
generate errors/warnings if the attribute is redundantly used; however,
where possible let's avoid it as it reduces preprocessed code size and
associated compile-time overheads.

[elver@google.com: Implement __has_feature(coverage_sanitizer) in Clang]
  Link: https://lkml.kernel.org/r/20210527162655.3246381-1-elver@google.com
[elver@google.com: add comment explaining __has_feature() in Clang]
  Link: https://lkml.kernel.org/r/20210527194448.3470080-1-elver@google.com

Link: https://lkml.kernel.org/r/20210525175819.699786-1-elver@google.com
Signed-off-by: Marco Elver 
Acked-by: Peter Zijlstra (Intel) 
Reviewed-by: Miguel Ojeda 
Reviewed-by: Nathan Chancellor 
Cc: Nick Desaulniers 
Cc: Kees Cook 
Cc: Will Deacon 
Cc: Ard Biesheuvel 
Cc: Luc Van Oostenryck 
Cc: Arvind Sankar 
Cc: Masahiro Yamada 
Cc: Sami Tolvanen 
Cc: Arnd Bergmann 
Cc: Dmitry Vyukov 
Cc: Mark Rutland 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin

cfi: add __cficanonical

2021-04-08T23:04:20+00:00

With CONFIG_CFI_CLANG, the compiler replaces a function address taken
in C code with the address of a local jump table entry, which passes
runtime indirect call checks. However, the compiler won't replace
addresses taken in assembly code, which will result in a CFI failure
if we later jump to such an address in instrumented C code. The code
generated for the non-canonical jump table looks this:

  : /* In C, &noncanonical points here */
	jmp noncanonical
  ...
  :        /* function body */
	...

This change adds the __cficanonical attribute, which tells the
compiler to use a canonical jump table for the function instead. This
means the compiler will rename the actual function to .cfi
and points the original symbol to the jump table entry instead:

  :           /* jump table entry */
	jmp canonical.cfi
  ...
  :       /* function body */
	...

As a result, the address taken in assembly, or other non-instrumented
code always points to the jump table and therefore, can be used for
indirect calls in instrumented code without tripping CFI checks.

Signed-off-by: Sami Tolvanen 
Reviewed-by: Kees Cook 
Acked-by: Bjorn Helgaas    # pci.h
Tested-by: Nathan Chancellor 
Signed-off-by: Kees Cook 
Link: https://lore.kernel.org/r/20210408182843.1754385-3-samitolvanen@google.com

add support for Clang CFI

2021-04-08T23:04:20+00:00

This change adds support for Clang’s forward-edge Control Flow
Integrity (CFI) checking. With CONFIG_CFI_CLANG, the compiler
injects a runtime check before each indirect function call to ensure
the target is a valid function with the correct static type. This
restricts possible call targets and makes it more difficult for
an attacker to exploit bugs that allow the modification of stored
function pointers. For more details, see:

  https://clang.llvm.org/docs/ControlFlowIntegrity.html

Clang requires CONFIG_LTO_CLANG to be enabled with CFI to gain
visibility to possible call targets. Kernel modules are supported
with Clang’s cross-DSO CFI mode, which allows checking between
independently compiled components.

With CFI enabled, the compiler injects a __cfi_check() function into
the kernel and each module for validating local call targets. For
cross-module calls that cannot be validated locally, the compiler
calls the global __cfi_slowpath_diag() function, which determines
the target module and calls the correct __cfi_check() function. This
patch includes a slowpath implementation that uses __module_address()
to resolve call targets, and with CONFIG_CFI_CLANG_SHADOW enabled, a
shadow map that speeds up module look-ups by ~3x.

Clang implements indirect call checking using jump tables and
offers two methods of generating them. With canonical jump tables,
the compiler renames each address-taken function to .cfi
and points the original symbol to a jump table entry, which passes
__cfi_check() validation. This isn’t compatible with stand-alone
assembly code, which the compiler doesn’t instrument, and would
result in indirect calls to assembly code to fail. Therefore, we
default to using non-canonical jump tables instead, where the compiler
generates a local jump table entry .cfi_jt for each
address-taken function, and replaces all references to the function
with the address of the jump table entry.

Note that because non-canonical jump table addresses are local
to each component, they break cross-module function address
equality. Specifically, the address of a global function will be
different in each module, as it's replaced with the address of a local
jump table entry. If this address is passed to a different module,
it won’t match the address of the same function taken there. This
may break code that relies on comparing addresses passed from other
components.

CFI checking can be disabled in a function with the __nocfi attribute.
Additionally, CFI can be disabled for an entire compilation unit by
filtering out CC_FLAGS_CFI.

By default, CFI failures result in a kernel panic to stop a potential
exploit. CONFIG_CFI_PERMISSIVE enables a permissive mode, where the
kernel prints out a rate-limited warning instead, and allows execution
to continue. This option is helpful for locating type mismatches, but
should only be enabled during development.

Signed-off-by: Sami Tolvanen 
Reviewed-by: Kees Cook 
Tested-by: Nathan Chancellor 
Signed-off-by: Kees Cook 
Link: https://lore.kernel.org/r/20210408182843.1754385-2-samitolvanen@google.com

Merge tag 'compiler-attributes-for-linus-v5.11' of git://github.com/ojeda/linux

2021-01-04T18:47:38+00:00

Pull ENABLE_MUST_CHECK removal from Miguel Ojeda:
 "Remove CONFIG_ENABLE_MUST_CHECK (Masahiro Yamada)"

Note that this removes the config option by making the must-check
unconditional, not by removing must check itself.

* tag 'compiler-attributes-for-linus-v5.11' of git://github.com/ojeda/linux:
  Compiler Attributes: remove CONFIG_ENABLE_MUST_CHECK

Merge tag 'asm-generic-cleanup-5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic

2020-12-16T07:41:19+00:00

Pull asm-generic cleanups from Arnd Bergmann:
 "These are a couple of compiler warning fixes to make 'make W=2' less
  noisy, as well as some fixes to code comments in asm-generic"

* tag 'asm-generic-cleanup-5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic:
  syscalls: Fix file comments for syscalls implemented in kernel/sys.c
  ctype.h: remove duplicate isdigit() helper
  qspinlock: use signed temporaries for cmpxchg
  asm-generic: fix ffs -Wshadow warning
  asm-generic: percpu: avoid Wshadow warning
  asm-generic/sembuf: Update architecture related information in comment

Compiler Attributes: remove CONFIG_ENABLE_MUST_CHECK

2020-12-02T12:47:17+00:00

Revert commit cebc04ba9aeb ("add CONFIG_ENABLE_MUST_CHECK").

A lot of warn_unused_result warnings existed in 2006, but until now
they have been fixed thanks to people doing allmodconfig tests.

Our goal is to always enable __must_check where appropriate, so this
CONFIG option is no longer needed.

I see a lot of defconfig (arch/*/configs/*_defconfig) files having:

    # CONFIG_ENABLE_MUST_CHECK is not set

I did not touch them for now since it would be a big churn. If arch
maintainers want to clean them up, please go ahead.

While I was here, I also moved __must_check to compiler_attributes.h
from compiler_types.h

Signed-off-by: Masahiro Yamada 
Acked-by: Jason A. Donenfeld 
Acked-by: Nathan Chancellor 
Reviewed-by: Nick Desaulniers 
[Moved addition in compiler_attributes.h to keep it sorted]
Signed-off-by: Miguel Ojeda

bpf: Don't rely on GCC attribute((optimize)) to disable GCSE

2020-10-30T03:01:46+00:00

Commit 3193c0836 ("bpf: Disable GCC -fgcse optimization for
___bpf_prog_run()") introduced a __no_fgcse macro that expands to a
function scope __attribute__((optimize("-fno-gcse"))), to disable a
GCC specific optimization that was causing trouble on x86 builds, and
was not expected to have any positive effect in the first place.

However, as the GCC manual documents, __attribute__((optimize))
is not for production use, and results in all other optimization
options to be forgotten for the function in question. This can
cause all kinds of trouble, but in one particular reported case,
it causes -fno-asynchronous-unwind-tables to be disregarded,
resulting in .eh_frame info to be emitted for the function.

This reverts commit 3193c0836, and instead, it disables the -fgcse
optimization for the entire source file, but only when building for
X86 using GCC with CONFIG_BPF_JIT_ALWAYS_ON disabled. Note that the
original commit states that CONFIG_RETPOLINE=n triggers the issue,
whereas CONFIG_RETPOLINE=y performs better without the optimization,
so it is kept disabled in both cases.

Fixes: 3193c0836f20 ("bpf: Disable GCC -fgcse optimization for ___bpf_prog_run()")
Signed-off-by: Ard Biesheuvel 
Signed-off-by: Alexei Starovoitov 
Tested-by: Geert Uytterhoeven 
Reviewed-by: Nick Desaulniers 
Link: https://lore.kernel.org/lkml/CAMuHMdUg0WJHEcq6to0-eODpXPOywLot6UD2=GFHpzoj_hCoBQ@mail.gmail.com/
Link: https://lore.kernel.org/bpf/20201028171506.15682-2-ardb@kernel.org

ctype.h: remove duplicate isdigit() helper

2020-10-28T13:55:36+00:00

gcc warns a few thousand times about the isdigit() shadow:

include/linux/ctype.h:26:19: warning: declaration of 'isdigit' shadows a built-in function [-Wshadow]

As there is already a compiler builtin, just use that, and make
it clear we do that by defining a macro.  Unfortunately, clang
does not have the isdigit() builtin, so this has to be conditional.

Signed-off-by: Arnd Bergmann

sparse: use static inline for __chk_{user,io}_ptr()

2020-08-29T07:29:32+00:00

__chk_user_ptr() & __chk_io_ptr() are dummy extern functions which
only exist to enforce the typechecking of __user or __iomem pointers
in macros when using sparse.

This typechecking is done by inserting a call to these functions.
But the presence of these calls can inhibit some simplifications
and so influence the result of sparse's analysis of context/locking.

Fix this by changing these calls into static inline calls with
an empty body.

Signed-off-by: Luc Van Oostenryck 
Signed-off-by: Miguel Ojeda

sparse: group the defines by functionality

2020-08-12T17:57:59+00:00

By popular demand, reorder the defines for sparse annotations and group
them by functionality.

Signed-off-by: Luc Van Oostenryck 
Signed-off-by: Andrew Morton 
Acked-by: Miguel Ojeda 
Cc: Geert Uytterhoeven 
Link: lore.kernel.org/r/CAMuHMdWQsirja-h3wBcZezk+H2Q_HShhAks8Hc8ps5fTAp=ObQ@mail.gmail.com
Link: http://lkml.kernel.org/r/20200621143652.53798-1-luc.vanoostenryck@gmail.com
Signed-off-by: Linus Torvalds