linux-kernel - Re: [RFC PATCH 2/8] x86/fpu/xstate: Fix guest fpstate allocation size calculation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <ZTMcuOutjGOnjVIY@google.com>
Date:   Sat, 21 Oct 2023 00:35:04 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, tglx@...utronix.de, peterz@...radead.org,
        pbonzini@...hat.com, rick.p.edgecombe@...el.com,
        kvm@...r.kernel.org, yang.zhong@...el.com, jing2.liu@...el.com,
        chao.gao@...el.com
Subject: Re: [RFC PATCH 2/8] x86/fpu/xstate: Fix guest fpstate allocation size calculation

On Fri, Oct 20, 2023, Sean Christopherson wrote:
> On Wed, Sep 13, 2023, Yang Weijiang wrote:
> > Fix guest xsave area allocation size from fpu_user_cfg.default_size to
> > fpu_kernel_cfg.default_size so that the xsave area size is consistent
> > with fpstate->size set in __fpstate_reset().
> > 
> > With the fix, guest fpstate size is sufficient for KVM supported guest
> > xfeatures.
> > 
> > Fixes: 69f6ed1d14c6 ("x86/fpu: Provide infrastructure for KVM FPU cleanup");
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> > ---
> >  arch/x86/kernel/fpu/core.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> > index a86d37052a64..a42d8ad26ce6 100644
> > --- a/arch/x86/kernel/fpu/core.c
> > +++ b/arch/x86/kernel/fpu/core.c
> > @@ -220,7 +220,9 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
> >  	struct fpstate *fpstate;
> >  	unsigned int size;
> >  
> > -	size = fpu_user_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
> > +	size = fpu_kernel_cfg.default_size +
> > +	       ALIGN(offsetof(struct fpstate, regs), 64);
> 
> This looks sketchy and incomplete.  I haven't looked at the gory details of
> fpu_user_cfg vs. fpu_kernel_cfg, but the rest of this function uses fpu_user_cfg,
> including a check on fpu_user_cfg.default_size.  That makes me think that changing
> just the allocation size isn't quite right.

Shoot, I didn't realize the CET virtualization series included this a day later.
I'll respond there.