Re: [PATCH v2 1/3] x86/uprobes: Fix not using prefixes.nbytes for loop over prefixes.bytes

[Masami Hiramatsu <mhiramat@kernel.org>]

On Thu, 3 Dec 2020 13:37:57 +0100
Borislav Petkov <bp@alien8.de> wrote:

> On Thu, Dec 03, 2020 at 01:50:37PM +0900, Masami Hiramatsu wrote:
> > Since the insn.prefixes.nbytes can be bigger than the size of
> > insn.prefixes.bytes[] when a same prefix is repeated, we have to
> > check whether the insn.prefixes.bytes[i] != 0 and i < 4 instead
> > of insn.prefixes.nbytes.
> > This introduces for_each_insn_prefix() macro for this purpose.
> > 
> > Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints")
> > Reported-by: syzbot+9b64b619f10f19d19a7c@syzkaller.appspotmail.com
> > Debugged-by: Kees Cook <keescook@chromium.org>
> > Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > Cc: stable@vger.kernel.org
> > ---
> >  Changes in v2:
> >   - Add for_each_insn_prefix() macro and fix to check index first.
> > ---
> >  arch/x86/include/asm/insn.h |   15 +++++++++++++++
> >  arch/x86/kernel/uprobes.c   |   10 ++++++----
> >  2 files changed, 21 insertions(+), 4 deletions(-)
> 
> Warning: Kernel ABI header at 'tools/arch/x86/include/asm/insn.h' differs from latest version at 'arch/x86/include/asm/insn.h'

Oops.

> 
> > diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h
> > index 5c1ae3eff9d4..e6b38ebd3a1c 100644
> > --- a/arch/x86/include/asm/insn.h
> > +++ b/arch/x86/include/asm/insn.h
> > @@ -201,6 +201,21 @@ static inline int insn_offset_immediate(struct insn *insn)
> >  	return insn_offset_displacement(insn) + insn->displacement.nbytes;
> >  }
> >  
> > +/**
> > + * for_each_insn_prefix() -- Iterate prefixes in the instruction
> > + * @insn: Pointer to struct insn.
> > + * @idx:  Index storage.
> > + * @prefix: Prefix byte.
> > + *
> > + * Iterate prefix bytes of given @insn. Each prefix byte is stored in @prefix
> > + * and the index is stored in @idx (note that this @idx is just for a cursor,
> > + * do not change it.)
> > + * Since prefixes.nbytes can be bigger than 4 if some prefixes are repeated,
> > + * we can not use it for looping over the prefixes.
> 
> Please use passive voice: no "we" or "I", etc,

OK.

> 
> > + */
> > +#define for_each_insn_prefix(insn, idx, prefix)	\
> > +	for (idx = 0; idx < 4 && (prefix = insn->prefixes.bytes[idx]) != 0; idx++)
> 
> Btw, looking at the struct insn definition, that prefixes member should
> have a comment above it that those are the legacy prefixes which can be
> <= 4. But that's minor.
> 
> In any case, I'll fix up the minor issues now but pls remember to do
> them in the future.

OK, I will add a macro with comment for it.

Thank you,

> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette


-- 
Masami Hiramatsu <mhiramat@kernel.org>