linux-kernel - Re: [RFC PATCH v4 21/27] x86/cet/shstk: ELF header parsing of Shadow Stack

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Date:   Tue, 09 Oct 2018 14:15:14 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Eugene Syromiatnikov <esyr@...hat.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Subject: Re: [RFC PATCH v4 21/27] x86/cet/shstk: ELF header parsing of
 Shadow Stack

On Thu, 2018-10-04 at 01:27 +0200, Eugene Syromiatnikov wrote:
> On Fri, Sep 21, 2018 at 08:03:45AM -0700, Yu-cheng Yu wrote:

[...]

> > diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
> > index 0d157d2a1e2a..5b5f169c5c07 100644
> > --- a/arch/x86/include/asm/elf.h
> > +++ b/arch/x86/include/asm/elf.h
> > @@ -382,4 +382,9 @@ struct va_alignment {
> >  
> >  extern struct va_alignment va_align;
> >  extern unsigned long align_vdso_addr(unsigned long);
> > +
> > +#ifdef CONFIG_ARCH_HAS_PROGRAM_PROPERTIES
> > +extern int arch_setup_features(void *ehdr, void *phdr, struct file *file,
> > +			       bool interp);
> > +#endif
> >  #endif /* _ASM_X86_ELF_H */
> > diff --git a/arch/x86/include/uapi/asm/elf_property.h
> > b/arch/x86/include/uapi/asm/elf_property.h
> > new file mode 100644
> > index 000000000000..af361207718c
> > --- /dev/null
> > +++ b/arch/x86/include/uapi/asm/elf_property.h
> > @@ -0,0 +1,15 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef _UAPI_ASM_X86_ELF_PROPERTY_H
> > +#define _UAPI_ASM_X86_ELF_PROPERTY_H
> > +
> > +/*
> > + * pr_type
> > + */
> > +#define GNU_PROPERTY_X86_FEATURE_1_AND (0xc0000002)
> > +
> > +/*
> > + * Bits for GNU_PROPERTY_X86_FEATURE_1_AND
> > + */
> > +#define GNU_PROPERTY_X86_FEATURE_1_SHSTK	(0x00000002)
> 
> Hm, these defeinitions aren't much different comparing to NT_*
> definitions in include/uapi/linux/elf.h, is it expected that those
> properties have to be parsed individually for each architecture?

Yes, we have NT_GNU_PROPERTY_TYPE_0 defined in include/uapi/linux/elf.h.
GNU_PROPERTY_X86_FEATURE_1_xxxx is for X86 only.

[...]

> 
> There's a lot of similar code with bpf stackmap .build-id code (commit
> v4.17-rc1~148^2~156^2~3^2~1), it might be worthy generalising some ELF
> traversal routines, since there's general need of parsing ELF property
> segments.

Only a small similarity exists.  The routine find_note_type_0() does a lot more
validation.  It appears stack_map_get_build_id() does not need that.

Yu-cheng