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Date: Tue, 10 May 2022 15:01:22 -0700 From: Kees Cook <keescook@...omium.org> To: Andrew Morton <akpm@...ux-foundation.org> Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>, linux-mm@...ck.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH 1/4] mm/usercopy: Check kmap addresses properly On Mon, May 09, 2022 at 08:37:42PM -0700, Andrew Morton wrote: > On Mon, 10 Jan 2022 23:15:27 +0000 "Matthew Wilcox (Oracle)" <willy@...radead.org> wrote: > > > If you are copying to an address in the kmap region, you may not copy > > across a page boundary, > > In the source, the destination or in both, and why may we not? This depends on direction. For copying to userspace, the source (kmap). For copying from userspace, the destination (kmap). > > no matter what the size of the underlying > > allocation. You can't kmap() a slab page because slab pages always > > come from low memory. As in it'll be processed as a slab page instead of kmap by the usercopy checks? -- Kees Cook
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