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Message-ID: <Yy5MmwVWD7IxCQi2@work> Date: Fri, 23 Sep 2022 19:17:31 -0500 From: "Gustavo A. R. Silva" <gustavoars@...nel.org> To: Kees Cook <keescook@...omium.org> Cc: Miguel Ojeda <ojeda@...nel.org>, Siddhesh Poyarekar <siddhesh@...plt.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Nathan Chancellor <nathan@...nel.org>, Tom Rix <trix@...hat.com>, llvm@...ts.linux.dev, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] Compiler Attributes: Introduce __access_*() function attribute On Fri, Sep 23, 2022 at 04:54:24PM -0700, Kees Cook wrote: > Added in GCC 10.1, the "access" function attribute 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. While it is legal to provide only the pointer argument > position and access type, design the kernel macros 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, > u8 *src, int src_len); > > (And if "dst" will also be read, it could use __access_rw(2, 3) instead.) > > These can inform the compile-time diagnostics of GCC including > -Warray-bounds, -Wstringop-overflow, etc, and can affect > __builtin_dynamic_object_size() results. > > Cc: Miguel Ojeda <ojeda@...nel.org> > Cc: Siddhesh Poyarekar <siddhesh@...plt.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> Acked-by: Gustavo A. R. Silva <gustavoars@...nel.org> -- Gustavo > --- > include/linux/compiler_attributes.h | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h > index 9a9907fad6fd..6f3d40f7ee5e 100644 > --- a/include/linux/compiler_attributes.h > +++ b/include/linux/compiler_attributes.h > @@ -20,6 +20,22 @@ > * 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 > + */ > +#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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