linux-kernel - Re: [PATCH V3] ZBOOT: fix stack protector in compressed boot phase

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Date:   Fri, 23 Mar 2018 11:50:55 +0800
From:   Jiaxun Yang <jiaxun.yang@...goat.com>
To:     James Hogan <jhogan@...nel.org>, Huacai Chen <chenhc@...ote.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>,
        linux-mips@...ux-mips.org, Russell King <linux@....linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH V3] ZBOOT: fix stack protector in compressed boot phase

在 2018-03-22四的 22:21 +0000，James Hogan写道：
> On Fri, Mar 16, 2018 at 03:55:16PM +0800, Huacai Chen wrote:
> > diff --git a/arch/mips/boot/compressed/decompress.c
> > b/arch/mips/boot/compressed/decompress.c
> > index fdf99e9..5ba431c 100644
> > --- a/arch/mips/boot/compressed/decompress.c
> > +++ b/arch/mips/boot/compressed/decompress.c
> > @@ -78,11 +78,6 @@ void error(char *x)
> >  
> >  unsigned long __stack_chk_guard;
> 
> ...
> 
> > diff --git a/arch/mips/boot/compressed/head.S
> > b/arch/mips/boot/compressed/head.S
> > index 409cb48..00d0ee0 100644
> > --- a/arch/mips/boot/compressed/head.S
> > +++ b/arch/mips/boot/compressed/head.S
> > @@ -32,6 +32,10 @@ start:
> >  	bne	a2, a0, 1b
> >  	 addiu	a0, a0, 4
> >  
> > +	PTR_LA	a0, __stack_chk_guard
> > +	PTR_LI	a1, 0x000a0dff
> > +	sw	a1, 0(a0)
> 

Hi James

Huacai Can't reply this mail. His chenhc@...ote.com is blcoked by
Linux-MIPS mailing list while his Gmail didn't receive this email, so
I'm replying for him.

> Should that not be LONG_S? Otherwise big endian MIPS64 would get a
> word-swapped canary (which is probably mostly harmless, but still).

Yes, he said it's considerable.

> 
> Also I think it worth mentioning in the commit message the MIPS
> configuration you hit this with, presumably a Loongson one? For me
> decompress_kernel() gets a stack guard on loongson3_defconfig, but
> not
> malta_defconfig or malta_defconfig + 64-bit. I presume its sensitive
> to
> the compiler inlining stuff into decompress_kernel() or something
> such
> that it suddenly qualifies for a stack guard.

Have you tested with CONFIG_CC_STACKPROTECTOR_STRONG=y ?
Huacai reproduced the issue by this[1] config with GCC 4.9.

[1] https://github.com/loongson-community/linux-stable/blob/rebase-4.14
/arch/mips/configs/loongson3_defconfig

> 
> Cheers
> James