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Linus Torvalds 6014bc2756 x86-64: make access_ok() independent of LAM 
The linear address masking (LAM) code made access_ok() more complicated,
in that it now needs to untag the address in order to verify the access
range.  See commit 74c228d20a ("x86/uaccess: Provide untagged_addr()
and remove tags before address check").

We were able to avoid that overhead in the get_user/put_user code paths
by simply using the sign bit for the address check, and depending on the
GP fault if the address was non-canonical, which made it all independent
of LAM.

And we can do the same thing for access_ok(): simply check that the user
pointer range has the high bit clear.  No need to bother with any
address bit masking.

In fact, we can go a bit further, and just check the starting address
for known small accesses ranges: any accesses that overflow will still
be in the non-canonical area and will still GP fault.

To still make syzkaller catch any potentially unchecked user addresses,
we'll continue to warn about GP faults that are caused by accesses in
the non-canonical range.  But we'll limit that to purely "high bit set
and past the one-page 'slop' area".

We could probably just do that "check only starting address" for any
arbitrary range size: realistically all kernel accesses to user space
will be done starting at the low address.  But let's leave that kind of
optimization for later.  As it is, this already allows us to generate
simpler code and not worry about any tag bits in the address.

The one thing to look out for is the GUP address check: instead of
actually copying data in the virtual address range (and thus bad
addresses being caught by the GP fault), GUP will look up the page
tables manually.  As a result, the page table limits need to be checked,
and that was previously implicitly done by the access_ok().

With the relaxed access_ok() check, we need to just do an explicit check
for TASK_SIZE_MAX in the GUP code instead.  The GUP code already needs
to do the tag bit unmasking anyway, so there this is all very
straightforward, and there are no LAM issues.

Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2023-05-03 10:37:22 -07:00
arch x86-64: make access_ok() independent of LAM 2023-05-03 10:37:22 -07:00
block Driver core changes for 6.4-rc1 2023-04-27 11:53:57 -07:00
certs KEYS: Add missing function documentation 2023-04-24 16:15:52 +03:00
crypto modules-6.4-rc1 2023-04-27 16:36:55 -07:00
Documentation Pin control bulk changes for the v6.4 kernel: 2023-05-02 15:40:41 -07:00
drivers Pin control bulk changes for the v6.4 kernel: 2023-05-02 15:40:41 -07:00
fs afs: Avoid endless loop if file is larger than expected 2023-05-02 17:23:50 +01:00
include VFIO updates for v6.4-rc1 2023-05-02 11:56:43 -07:00
init Objtool changes for v6.4: 2023-04-28 14:02:54 -07:00
io_uring Networking changes for 6.4. 2023-04-26 16:07:23 -07:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel IOMMU Updates for Linux 6.4 2023-04-30 13:00:38 -07:00
lib s390 updates for the 6.4 merge window 2023-04-30 11:43:31 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm x86-64: make access_ok() independent of LAM 2023-05-03 10:37:22 -07:00
net NFSD 6.4 Release Notes 2023-04-29 11:04:14 -07:00
rust Rust changes for v6.4 2023-04-30 11:20:22 -07:00
samples Rust changes for v6.4 2023-04-30 11:20:22 -07:00
scripts Kbuild updates for v6.4 2023-04-30 11:32:53 -07:00
security integrity-v6.4 2023-04-29 10:11:32 -07:00
sound Mainly singleton patches all over the place. Series of note are: 2023-04-27 19:57:00 -07:00
tools s390: 2023-05-01 12:06:20 -07:00
usr initramfs: Check negative timestamp to prevent broken cpio archive 2023-04-16 17:37:01 +09:00
virt s390: 2023-05-01 12:06:20 -07:00
.clang-format cxl for v6.4 2023-04-30 11:51:51 -07:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for *.dtso files 2023-02-26 15:28:23 +09:00
.gitignore linux-kselftest-kunit-6.4-rc1 2023-04-24 12:31:32 -07:00
.mailmap Mainly singleton patches all over the place. Series of note are: 2023-04-27 19:57:00 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Char/Misc drivers for 6.4-rc1 2023-04-27 12:07:50 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Pin control bulk changes for the v6.4 kernel: 2023-05-02 15:40:41 -07:00
Makefile Kbuild updates for v6.4 2023-04-30 11:32:53 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.