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Message-ID: <Yy/dLihBWSFzZdyq@dev-arch.thelio-3990X> Date: Sat, 24 Sep 2022 21:46:38 -0700 From: Nathan Chancellor <nathan@...nel.org> To: Kees Cook <keescook@...omium.org> Cc: Miguel Ojeda <ojeda@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, llvm@...ts.linux.dev, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH v2] Compiler Attributes: Introduce __access_*() function attribute On Sat, Sep 24, 2022 at 08:07:15AM -0700, Kees Cook wrote: > Added in GCC 10.1, the "access" function attribute is used to mark pointer > arguments for how they are expected to be accessed in a given function. > Both their access type (read/write, read-only, or write-only) and bounds > are specified. > > These can improve GCC's compile-time diagnostics including -Warray-bounds, > -Wstringop-overflow, etc, and can affect __builtin_dynamic_object_size() > results. > > Cc: Miguel Ojeda <ojeda@...nel.org> > Cc: Nick Desaulniers <ndesaulniers@...gle.com> > Cc: Nathan Chancellor <nathan@...nel.org> > Cc: Tom Rix <trix@...hat.com> > Cc: llvm@...ts.linux.dev > Signed-off-by: Kees Cook <keescook@...omium.org> The GCC docs say it is 'access', instead of '__access__'. I assume it is probably okay so: Reviewed-by: Nathan Chancellor <nathan@...nel.org> > --- > include/linux/compiler_attributes.h | 30 +++++++++++++++++++++++++++++ > 1 file changed, 30 insertions(+) > > diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h > index 9a9907fad6fd..465be5f072ff 100644 > --- a/include/linux/compiler_attributes.h > +++ b/include/linux/compiler_attributes.h > @@ -20,6 +20,36 @@ > * Provide links to the documentation of each supported compiler, if it exists. > */ > > +/* > + * Optional: only supported since gcc >= 10 > + * Optional: not supported by Clang > + * > + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-access-function-attribute > + * > + * While it is legal to provide only the pointer argument position and > + * access type, the kernel macros are designed to require also the bounds > + * (element count) argument position; if a function has no bounds argument, > + * refactor the code to include one. > + * > + * These can be used multiple times. For example: > + * > + * __access_wo(2, 3) __access_ro(4, 5) > + * int copy_something(struct context *ctx, u32 *dst, size_t dst_count, > + * const u8 *src, int src_len); > + * > + * If "dst" will also be read from, it could use __access_rw(2, 3) instead. > + * > + */ > +#if __has_attribute(__access__) > +# define __access_rw(ptr, count) __attribute__((__access__(read_write, ptr, count))) > +# define __access_ro(ptr, count) __attribute__((__access__(read_only, ptr, count))) > +# define __access_wo(ptr, count) __attribute__((__access__(write_only, ptr, count))) > +#else > +# define __access_rw(ptr, count) > +# define __access_ro(ptr, count) > +# define __access_wo(ptr, count) > +#endif > + > /* > * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alias-function-attribute > */ > -- > 2.34.1 >
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