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Message-ID: <202209240757.3AC47AC6@keescook> Date: Sat, 24 Sep 2022 07:58:54 -0700 From: Kees Cook <keescook@...omium.org> To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com> 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 Sat, Sep 24, 2022 at 12:06:31PM +0200, Miguel Ojeda wrote: > On Sat, Sep 24, 2022 at 1:54 AM Kees Cook <keescook@...omium.org> wrote: > > > > 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. > > Should this bit be included in the comment of the attribute? (since it > is specific to the kernel) Sure; good idea! > > > 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.) > > Also maybe the example could be nice there too, since it uses the > syntax for the kernel and you took the time to write it :) > > By the way, shouldn't `src` typically be `const u8 *`? Given it is an > example, I would qualify it. Yeah, I will update this. > > > +#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 > > If you do a v2 for the above, please take the chance to indent with a > single space after the `#` (like `# define`) for consistency. Fixed! I will send a v2. -- Kees Cook
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