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Re: [Xen-devel] [RFC 16/22] x86/percpu: Adapt percpu for PIE support
- To: Thomas Garnier <thgarnie@xxxxxxxxxx>
- From: Kees Cook <keescook@xxxxxxxxxxxx>
- Date: Wed, 2 Aug 2017 09:56:32 -0700
- Cc: Michal Hocko <mhocko@xxxxxxxx>, kvm list <kvm@xxxxxxxxxxxxxxx>, Radim Krčmář <rkrcmar@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Christopher Li <sparse@xxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>, Pavel Machek <pavel@xxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Kernel Hardening <kernel-hardening@xxxxxxxxxxxxxxxxxx>, Christoph Lameter <cl@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, linux-arch <linux-arch@xxxxxxxxxxxxxxx>, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>, Daniel Borkmann <daniel@xxxxxxxxxxxxx>, Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, Peter Foley <pefoley2@xxxxxxxxxxx>, Christian Borntraeger <borntraeger@xxxxxxxxxx>, linux-sparse@xxxxxxxxxxxxxxx, Matthias Kaehlcke <mka@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Borislav Petkov <bp@xxxxxxx>, Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>, Len Brown <len.brown@xxxxxxxxx>, Chris Metcalf <cmetcalf@xxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, linux-pm <linux-pm@xxxxxxxxxxxxxxx>, Brian Gerst <brgerst@xxxxxxxxx>, "H . J . Lu" <hjl.tools@xxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>, Paul Bolle <pebolle@xxxxxxxxxx>, "Paul E . McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>, Baoquan He <bhe@xxxxxxxxxx>, Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>, Jiri Kosina <jkosina@xxxxxxx>, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>, "Rafael J . Wysocki" <rjw@xxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Daniel Micay <danielmicay@xxxxxxxxx>, "linux-crypto@xxxxxxxxxxxxxxx" <linux-crypto@xxxxxxxxxxxxxxx>, Rob Landley <rob@xxxxxxxxxxx>, Tejun Heo <tj@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>, "David S . Miller" <davem@xxxxxxxxxxxxx>, "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
- Delivery-date: Wed, 02 Aug 2017 16:56:49 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On Wed, Aug 2, 2017 at 9:42 AM, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote:
> I noticed that not only we have the problem of gs:0x40 not being
> accessible. The compiler will default to the fs register if
> mcmodel=kernel is not set.
>
> On the next patch set, I am going to add support for
> -mstack-protector-guard=global so a global variable can be used
> instead of the segment register. Similar approach than ARM/ARM64.
While this is probably understood, I have to point out that this would
be a major regression for the stack protection on x86.
> Following this patch, I will work with gcc and llvm to add
> -mstack-protector-reg=<segment register> support similar to PowerPC.
> This way we can have gs used even without mcmodel=kernel. Once that's
> an option, I can setup the GDT as described in the previous email
> (similar to RFG).
It would be much nicer if we could teach gcc about the percpu area
instead. This would let us solve the global stack protector problem on
the other architectures:
http://www.openwall.com/lists/kernel-hardening/2017/06/27/6
-Kees
--
Kees Cook
Pixel Security
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