cve/published/2022/CVE-2022-49721.mbox

From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: <linux-cve-announce@vger.kernel.org>
Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org>
Subject: CVE-2022-49721: arm64: ftrace: consistently handle PLTs.

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

arm64: ftrace: consistently handle PLTs.

Sometimes it is necessary to use a PLT entry to call an ftrace
trampoline. This is handled by ftrace_make_call() and ftrace_make_nop(),
with each having *almost* identical logic, but this is not handled by
ftrace_modify_call() since its introduction in commit:

  3b23e4991fb66f6d ("arm64: implement ftrace with regs")

Due to this, if we ever were to call ftrace_modify_call() for a callsite
which requires a PLT entry for a trampoline, then either:

a) If the old addr requires a trampoline, ftrace_modify_call() will use
   an out-of-range address to generate the 'old' branch instruction.
   This will result in warnings from aarch64_insn_gen_branch_imm() and
   ftrace_modify_code(), and no instructions will be modified. As
   ftrace_modify_call() will return an error, this will result in
   subsequent internal ftrace errors.

b) If the old addr does not require a trampoline, but the new addr does,
   ftrace_modify_call() will use an out-of-range address to generate the
   'new' branch instruction. This will result in warnings from
   aarch64_insn_gen_branch_imm(), and ftrace_modify_code() will replace
   the 'old' branch with a BRK. This will result in a kernel panic when
   this BRK is later executed.

Practically speaking, case (a) is vastly more likely than case (b), and
typically this will result in internal ftrace errors that don't
necessarily affect the rest of the system. This can be demonstrated with
an out-of-tree test module which triggers ftrace_modify_call(), e.g.

| # insmod test_ftrace.ko
| test_ftrace: Function test_function raw=0xffffb3749399201c, callsite=0xffffb37493992024
| branch_imm_common: offset out of range
| branch_imm_common: offset out of range
| ------------[ ftrace bug ]------------
| ftrace failed to modify
| [<ffffb37493992024>] test_function+0x8/0x38 [test_ftrace]
|  actual:   1d:00:00:94
| Updating ftrace call site to call a different ftrace function
| ftrace record flags: e0000002
|  (2) R
|  expected tramp: ffffb374ae42ed54
| ------------[ cut here ]------------
| WARNING: CPU: 0 PID: 165 at kernel/trace/ftrace.c:2085 ftrace_bug+0x280/0x2b0
| Modules linked in: test_ftrace(+)
| CPU: 0 PID: 165 Comm: insmod Not tainted 5.19.0-rc2-00002-g4d9ead8b45ce #13
| Hardware name: linux,dummy-virt (DT)
| pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : ftrace_bug+0x280/0x2b0
| lr : ftrace_bug+0x280/0x2b0
| sp : ffff80000839ba00
| x29: ffff80000839ba00 x28: 0000000000000000 x27: ffff80000839bcf0
| x26: ffffb37493994180 x25: ffffb374b0991c28 x24: ffffb374b0d70000
| x23: 00000000ffffffea x22: ffffb374afcc33b0 x21: ffffb374b08f9cc8
| x20: ffff572b8462c000 x19: ffffb374b08f9000 x18: ffffffffffffffff
| x17: 6c6c6163202c6331 x16: ffffb374ae5ad110 x15: ffffb374b0d51ee4
| x14: 0000000000000000 x13: 3435646532346561 x12: 3437336266666666
| x11: 203a706d61727420 x10: 6465746365707865 x9 : ffffb374ae5149e8
| x8 : 336266666666203a x7 : 706d617274206465 x6 : 00000000fffff167
| x5 : ffff572bffbc4a08 x4 : 00000000fffff167 x3 : 0000000000000000
| x2 : 0000000000000000 x1 : ffff572b84461e00 x0 : 0000000000000022
| Call trace:
|  ftrace_bug+0x280/0x2b0
|  ftrace_replace_code+0x98/0xa0
|  ftrace_modify_all_code+0xe0/0x144
|  arch_ftrace_update_code+0x14/0x20
|  ftrace_startup+0xf8/0x1b0
|  register_ftrace_function+0x38/0x90
|  test_ftrace_init+0xd0/0x1000 [test_ftrace]
|  do_one_initcall+0x50/0x2b0
|  do_init_module+0x50/0x1f0
|  load_module+0x17c8/0x1d64
|  __do_sys_finit_module+0xa8/0x100
|  __arm64_sys_finit_module+0x2c/0x3c
|  invoke_syscall+0x50/0x120
|  el0_svc_common.constprop.0+0xdc/0x100
|  do_el0_svc+0x3c/0xd0
|  el0_svc+0x34/0xb0
|  el0t_64_sync_handler+0xbc/0x140
|  el0t_64_sync+0x18c/0x190
| ---[ end trace 0000000000000000 ]---

We can solve this by consistently determining whether to use a PLT entry
for an address.

Note that since (the earlier) commit:

  f1a54ae9af0da4d7 ("arm64: module/ftrace: intialize PLT at load time")

... we can consistently determine the PLT address that a given callsite
will use, and therefore ftrace_make_nop() does not need to skip
validation when a PLT is in use.

This patch factors the existing logic out of ftrace_make_call() and
ftrace_make_nop() into a common ftrace_find_callable_addr() helper
function, which is used by ftrace_make_call(), ftrace_make_nop(), and
ftrace_modify_call(). In ftrace_make_nop() the patching is consistently
validated by ftrace_modify_code() as we can always determine what the
old instruction should have been.

The Linux kernel CVE team has assigned CVE-2022-49721 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.5 with commit 3b23e4991fb66f6d152f9055ede271a726ef9f21 and fixed in 5.10.124 with commit bc28fde90937a920f7714ec4408269cac744f796
	Issue introduced in 5.5 with commit 3b23e4991fb66f6d152f9055ede271a726ef9f21 and fixed in 5.15.49 with commit db73aa9466338ec821ed2a0b01721fe4d06876b1
	Issue introduced in 5.5 with commit 3b23e4991fb66f6d152f9055ede271a726ef9f21 and fixed in 5.18.6 with commit dcecc96ed16f73417de5550f384e348c9d56f279
	Issue introduced in 5.5 with commit 3b23e4991fb66f6d152f9055ede271a726ef9f21 and fixed in 5.19 with commit a6253579977e4c6f7818eeb05bf2bc65678a7187

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2022-49721
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	arch/arm64/kernel/ftrace.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/bc28fde90937a920f7714ec4408269cac744f796
	https://git.kernel.org/stable/c/db73aa9466338ec821ed2a0b01721fe4d06876b1
	https://git.kernel.org/stable/c/dcecc96ed16f73417de5550f384e348c9d56f279
	https://git.kernel.org/stable/c/a6253579977e4c6f7818eeb05bf2bc65678a7187