linux-kernel - Re: [PATCH v2 2/4] KVM: selftests: Fix unaligned mmap allocations

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: <aQkZtjLt6lIULffA@google.com>
Date: Mon, 3 Nov 2025 13:08:06 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Jack Thomson <jackabt.amazon@...il.com>
Cc: maz@...nel.org, oliver.upton@...ux.dev, pbonzini@...hat.com, 
	joey.gouly@....com, suzuki.poulose@....com, yuzenghui@...wei.com, 
	catalin.marinas@....com, will@...nel.org, shuah@...nel.org, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	isaku.yamahata@...el.com, roypat@...zon.co.uk, kalyazin@...zon.co.uk, 
	jackabt@...zon.com
Subject: Re: [PATCH v2 2/4] KVM: selftests: Fix unaligned mmap allocations

On Tue, Oct 28, 2025, Jack Thomson wrote:
> 
> 
> On 23/10/2025 6:16 pm, Sean Christopherson wrote:
> > On Mon, Oct 13, 2025, Jack Thomson wrote:
> > > From: Jack Thomson <jackabt@...zon.com>
> > > 
> > > When creating a VM using mmap with huge pages, and the memory amount does
> > > not align with the underlying page size. The stored mmap_size value does
> > > not account for the fact that mmap will automatically align the length
> > > to a multiple of the underlying page size. During the teardown of the
> > > test, munmap is used. However, munmap requires the length to be a
> > > multiple of the underlying page size.
> > 
> > What happens when selftests use the wrong map_size?  E.g. is munmap() silently
> > failing?  If so, then I should probably take this particular patch through
> > kvm-x86/gmem, otherwise it means we'll start getting asserts due to:
> > 
> >    3223560c93eb ("KVM: selftests: Define wrappers for common syscalls to assert success")
> > 
> > If munmap() isn't failing, then that begs the question of what this patch is
> > actually doing :-)
> > 
> 
> Hi Sean, sorry I completely missed your reply.
> 
> Yeah currently with a misaligned map_size it causes munmap() to fail, I
> noticed when tested with different backings.

Exactly which tests fail?  I ask because I'm not sure we want to fix this by
having vm_mem_add() paper over test issues (I vaguely recall looking at this in
the past, but I can't find or recall the details).