linux-kernel - Re: [RFC PATCH v2 33/51] KVM: guest_memfd: Allocate and truncate from custom allocator

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

Message-ID: <CAGtprH-G6hA6dfFrRtFh+gazmr+27mvpoV-MNphbvKzm3WS4Rg@mail.gmail.com>
Date: Wed, 21 May 2025 11:05:32 -0700
From: Vishal Annapurve <vannapurve@...gle.com>
To: Ackerley Tng <ackerleytng@...gle.com>
Cc: kvm@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	x86@...nel.org, linux-fsdevel@...r.kernel.org, aik@....com, 
	ajones@...tanamicro.com, akpm@...ux-foundation.org, amoorthy@...gle.com, 
	anthony.yznaga@...cle.com, anup@...infault.org, aou@...s.berkeley.edu, 
	bfoster@...hat.com, binbin.wu@...ux.intel.com, brauner@...nel.org, 
	catalin.marinas@....com, chao.p.peng@...el.com, chenhuacai@...nel.org, 
	dave.hansen@...el.com, david@...hat.com, dmatlack@...gle.com, 
	dwmw@...zon.co.uk, erdemaktas@...gle.com, fan.du@...el.com, fvdl@...gle.com, 
	graf@...zon.com, haibo1.xu@...el.com, hch@...radead.org, hughd@...gle.com, 
	ira.weiny@...el.com, isaku.yamahata@...el.com, jack@...e.cz, 
	james.morse@....com, jarkko@...nel.org, jgg@...pe.ca, jgowans@...zon.com, 
	jhubbard@...dia.com, jroedel@...e.de, jthoughton@...gle.com, 
	jun.miao@...el.com, kai.huang@...el.com, keirf@...gle.com, 
	kent.overstreet@...ux.dev, kirill.shutemov@...el.com, liam.merwick@...cle.com, 
	maciej.wieczor-retman@...el.com, mail@...iej.szmigiero.name, maz@...nel.org, 
	mic@...ikod.net, michael.roth@....com, mpe@...erman.id.au, 
	muchun.song@...ux.dev, nikunj@....com, nsaenz@...zon.es, 
	oliver.upton@...ux.dev, palmer@...belt.com, pankaj.gupta@....com, 
	paul.walmsley@...ive.com, pbonzini@...hat.com, pdurrant@...zon.co.uk, 
	peterx@...hat.com, pgonda@...gle.com, pvorel@...e.cz, qperret@...gle.com, 
	quic_cvanscha@...cinc.com, quic_eberman@...cinc.com, 
	quic_mnalajal@...cinc.com, quic_pderrin@...cinc.com, quic_pheragu@...cinc.com, 
	quic_svaddagi@...cinc.com, quic_tsoni@...cinc.com, richard.weiyang@...il.com, 
	rick.p.edgecombe@...el.com, rientjes@...gle.com, roypat@...zon.co.uk, 
	rppt@...nel.org, seanjc@...gle.com, shuah@...nel.org, steven.price@....com, 
	steven.sistare@...cle.com, suzuki.poulose@....com, tabba@...gle.com, 
	thomas.lendacky@....com, usama.arif@...edance.com, vbabka@...e.cz, 
	viro@...iv.linux.org.uk, vkuznets@...hat.com, wei.w.wang@...el.com, 
	will@...nel.org, willy@...radead.org, xiaoyao.li@...el.com, 
	yan.y.zhao@...el.com, yilun.xu@...el.com, yuzenghui@...wei.com, 
	zhiquan1.li@...el.com
Subject: Re: [RFC PATCH v2 33/51] KVM: guest_memfd: Allocate and truncate from
 custom allocator

On Wed, May 14, 2025 at 4:43 PM Ackerley Tng <ackerleytng@...gle.com> wrote:
> ...
> +/**
> + * kvm_gmem_zero_range() - Zeroes all sub-pages in range [@start, @end).
> + *
> + * @mapping: the filemap to remove this range from.
> + * @start: index in filemap for start of range (inclusive).
> + * @end: index in filemap for end of range (exclusive).
> + *
> + * The pages in range may be split. truncate_inode_pages_range() isn't the right
> + * function because it removes pages from the page cache; this function only
> + * zeroes the pages.
> + */
> +static void kvm_gmem_zero_range(struct address_space *mapping,
> +                               pgoff_t start, pgoff_t end)
> +{
> +       struct folio_batch fbatch;
> +
> +       folio_batch_init(&fbatch);
> +       while (filemap_get_folios(mapping, &start, end - 1, &fbatch)) {
> +               unsigned int i;
> +
> +               for (i = 0; i < folio_batch_count(&fbatch); ++i) {
> +                       struct folio *f;
> +                       size_t nr_bytes;
> +
> +                       f = fbatch.folios[i];
> +                       nr_bytes = offset_in_folio(f, end << PAGE_SHIFT);
> +                       if (nr_bytes == 0)
> +                               nr_bytes = folio_size(f);
> +
> +                       folio_zero_segment(f, 0, nr_bytes);

folio_zero_segment takes byte offset and number of bytes within the
folio. This invocation needs to operate on the folio range that is
overlapping with [Start, end) and instead it's always starting from 0
and ending at an unaligned offset within the folio. This will result
in zeroing more than requested or lesser than requested or both
depending on the request and folio size.

> +               }
> +
> +               folio_batch_release(&fbatch);
> +               cond_resched();
> +       }
> +}
> +