Date: Mon, 28 Aug 2017 21:47:07 -0700 From: "Darrick J. Wong" <darrick.wong@...cle.com> To: Kees Cook <keescook@...omium.org> Cc: LKML <linux-kernel@...r.kernel.org>, David Windsor <dave@...lcore.net>, linux-xfs@...r.kernel.org, Linux-MM <linux-mm@...ck.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH v2 15/30] xfs: Define usercopy region in xfs_inode slab cache On Mon, Aug 28, 2017 at 02:57:14PM -0700, Kees Cook wrote: > On Mon, Aug 28, 2017 at 2:49 PM, Darrick J. Wong > <darrick.wong@...cle.com> wrote: > > On Mon, Aug 28, 2017 at 02:34:56PM -0700, Kees Cook wrote: > >> From: David Windsor <dave@...lcore.net> > >> > >> The XFS inline inode data, stored in struct xfs_inode_t field > >> i_df.if_u2.if_inline_data and therefore contained in the xfs_inode slab > >> cache, needs to be copied to/from userspace. > >> > >> cache object allocation: > >> fs/xfs/xfs_icache.c: > >> xfs_inode_alloc(...): > >> ... > >> ip = kmem_zone_alloc(xfs_inode_zone, KM_SLEEP); > >> > >> fs/xfs/libxfs/xfs_inode_fork.c: > >> xfs_init_local_fork(...): > >> ... > >> if (mem_size <= sizeof(ifp->if_u2.if_inline_data)) > >> ifp->if_u1.if_data = ifp->if_u2.if_inline_data; > > > > Hmm, what happens when mem_size > sizeof(if_inline_data)? A slab object > > will be allocated for ifp->if_u1.if_data which can then be used for > > readlink in the same manner as the example usage trace below. Does > > that allocated object have a need for a usercopy annotation like > > the one we're adding for if_inline_data? Or is that already covered > > elsewhere? > > Yeah, the xfs helper kmem_alloc() is used in the other case, which > ultimately boils down to a call to kmalloc(), which is entirely > whitelisted by an earlier patch in the series: > > https://lkml.org/lkml/2017/8/28/1026 Ah. It would've been helpful to have the first three patches cc'd to the xfs list. So basically this series establishes the ability to set regions within a slab object into which copy_to_user can copy memory contents, and vice versa. Have you seen any runtime performance impact? The overhead looks like it ought to be minimal. > (It's possible that at some future time we can start segregating > kernel-only kmallocs from usercopy-able kmallocs, but for now, there > are no plans for this.) A pity. It would be interesting to create no-usercopy versions of the kmalloc-* slabs and see how much of XFS' memory consumption never touches userspace buffers. :) --D > > -Kees > > -- > Kees Cook > Pixel Security > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
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