linux-kernel - Re: [PATCH v4 1/6] x86/elf: Add table to document READ_IMPLIES

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Message-ID: <202003121705.6ABA79D8F0@keescook>
Date:   Thu, 12 Mar 2020 17:06:01 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Jason Gunthorpe <jgg@...lanox.com>,
        Hector Marco-Gisbert <hecmargi@....es>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will@...nel.org>, Jann Horn <jannh@...gle.com>,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/6] x86/elf: Add table to document READ_IMPLIES_EXEC

On Wed, Mar 11, 2020 at 08:44:46PM +0100, Borislav Petkov wrote:
> Ozenn Mon, Feb 24, 2020 at 09:13:02PM -0800, Kees Cook wrote:
> > Add a table to document the current behavior of READ_IMPLIES_EXEC in
> > preparation for changing the behavior.
> > 
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > Reviewed-by: Jason Gunthorpe <jgg@...lanox.com>
> > ---
> >  arch/x86/include/asm/elf.h | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> > 
> > diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
> > index 69c0f892e310..733f69c2b053 100644
> > --- a/arch/x86/include/asm/elf.h
> > +++ b/arch/x86/include/asm/elf.h
> > @@ -281,6 +281,25 @@ extern u32 elf_hwcap2;
> >  /*
> >   * An executable for which elf_read_implies_exec() returns TRUE will
> >   * have the READ_IMPLIES_EXEC personality flag set automatically.
> > + *
> > + * The decision process for determining the results are:
> > + *
> > + *              CPU: | lacks NX*  | has NX, ia32     | has NX, x86_64 |
> > + * ELF:              |            |                  |                |
> > + * -------------------------------|------------------|----------------|
> > + * missing GNU_STACK | exec-all   | exec-all         | exec-all       |
> > + * GNU_STACK == RWX  | exec-all   | exec-all         | exec-all       |
> > + * GNU_STACK == RW   | exec-none  | exec-none        | exec-none      |
> 
> In all those tables, you wanna do:
> 
> s/GNU_STACK/PT_GNU_STACK/g
> 
> so that it is clear what this define is.

Fair enough. :) I think I was trying to save 3 characters from earlier
tables that were wider. I'll send a v5.

Thanks!

-Kees

-- 
Kees Cook