linux-kernel - Re: [PATCH v2] kvm: Fix warning in__kvm_gpc

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Date: Fri, 28 Jun 2024 16:00:22 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: paul@....org, Pei Li <peili.dev@...il.com>, Sean Christopherson
 <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner
 <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
 <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling
 <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linuxfoundation.org, 
	syzkaller-bugs@...glegroups.com, llvm@...ts.linux.dev, 
	syzbot+fd555292a1da3180fc82@...kaller.appspotmail.com
Subject: Re: [PATCH v2] kvm: Fix warning in__kvm_gpc_refresh

On Fri, 2024-06-28 at 15:25 +0100, Paul Durrant wrote:
> On 27/06/2024 16:03, Pei Li wrote:
> > Check for invalid hva address stored in data and return -EINVAL before
> > calling into __kvm_gpc_activate().
> > 
> > Reported-by: syzbot+fd555292a1da3180fc82@...kaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82
> > Tested-by: syzbot+fd555292a1da3180fc82@...kaller.appspotmail.com
> > Signed-off-by: Pei Li <peili.dev@...il.com>
> > ---
> > Syzbot reports a warning message in __kvm_gpc_refresh(). This warning
> > requires at least one of gpa and uhva to be valid.
> > WARNING: CPU: 0 PID: 5090 at arch/x86/kvm/../../../virt/kvm/pfncache.c:259 __kvm_gpc_refresh+0xf17/0x1090 arch/x86/kvm/../../../virt/kvm/pfncache.c:259
> > 
> > We are calling it from kvm_gpc_activate_hva(). This function always calls
> > __kvm_gpc_activate() with INVALID_GPA. Thus, uhva must be valid to
> > disable this warning.
> > 
> > This patch checks for invalid hva address and return -EINVAL before
> > calling __kvm_gpc_activate().
> > 
> > syzbot has tested the proposed patch and the reproducer did not trigger
> > any issue.
> > 
> > Tested on:
> > 
> > commit:         afcd4813 Merge tag 'mm-hotfixes-stable-2024-06-26-17-2..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1427e301980000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=e40800950091403a
> > dashboard link: https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > patch:          https://syzkaller.appspot.com/x/patch.diff?x=13838f3e980000
> > 
> > Note: testing is done by a robot and is best-effort only.
> > ---
> > Changes in v2:
> > - Adapted Sean's suggestion to check for valid address before calling
> >    into __kvm_gpc_activate().
> > - Link to v1: https://lore.kernel.org/r/20240625-bug5-v1-1-e072ed5fce85@gmail.com
> > ---
> >   arch/x86/kvm/xen.c  | 2 +-
> >   virt/kvm/pfncache.c | 3 +++
> >   2 files changed, 4 insertions(+), 1 deletion(-)
> > 
> 
> Reviewed-by: Paul Durrant <paul@....org>

Reviewed-by: David Woodhouse <dwmw@...zon.co.uk>

Thanks.

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