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Message-ID: <1485448847.14852.2.camel@opteya.com>
Date: Thu, 26 Jan 2017 17:40:47 +0100
From: Yann Droneaud <ydroneaud@...eya.com>
To: Will Deacon <will.deacon@....com>, kpark3469@...il.com
Cc: kernel-hardening@...ts.openwall.com, catalin.marinas@....com,
keescook@...omium.org, mark.rutland@....com, james.morse@....com,
panand@...hat.com, keun-o.park@...kmatter.ae, takahiro.akashi@...aro.org
Subject: Re: Re: [PATCH] arm64: usercopy: Implement stack
frame object validation
Hi,
Le mercredi 25 janvier 2017 à 13:54 +0000, Will Deacon a écrit :
> diff --git a/arch/arm64/include/asm/thread_info.h
> > b/arch/arm64/include/asm/thread_info.h
> > index 46c3b93..f610c44 100644
> > --- a/arch/arm64/include/asm/thread_info.h
> > +++ b/arch/arm64/include/asm/thread_info.h
> > @@ -68,7 +68,62 @@ struct thread_info {
> > + const void *oldframe;
> > + const void *callee_fp = NULL;
> > + const void *caller_fp = NULL;
> > +
> > + oldframe = __builtin_frame_address(1);
> > + if (oldframe) {
> > + callee_fp = __builtin_frame_address(2);
> > + if (callee_fp)
> > + caller_fp = __builtin_frame_address(3);
> > + }
> >
> Which compilers have you tested this with? The GCC folks don't
> guarantee a frame layout, and they have changed it in the past, so I
> suspect this is pretty fragile. In particularly, if
> __builtin_frame_address just points at the frame record, then I don't
> think you can make assumptions about the placement of local variables
> and arguments with respect to that.
>
https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gcc/Return-Address.html#index-
g_t_005f_005fbuiltin_005fframe_005faddress-3701
"Calling this function with a nonzero argument can have unpredictable
effects, including crashing the calling program. As a result, calls
that are considered unsafe are diagnosed when the -Wframe-address
option is in effect. Such calls should only be made in debugging
situations."
--
Yann Droneaud
OPTEYA
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