From 251959e47018b4696ccbef32f5502f0f810603f4 Mon Sep 17 00:00:00 2001
From: Russell Currey <ruscur@russell.cc>
Date: Wed, 27 Oct 2021 17:24:10 +1000
Subject: [PATCH] powerpc/security: Use a mutex for interrupt exit code patching
Git-commit: 3c12b4df8d5e026345a19886ae375b3ebc33c0b6
Patch-mainline: v5.16-rc1
References: stable-5.14.19 bsc#1193470 ltc#195599
commit 3c12b4df8d5e026345a19886ae375b3ebc33c0b6 upstream.
The mitigation-patching.sh script in the powerpc selftests toggles
all mitigations on and off simultaneously, revealing that rfi_flush
and stf_barrier cannot safely operate at the same time due to races
in updating the static key.
On some systems, the static key code throws a warning and the kernel
remains functional. On others, the kernel will hang or crash.
Fix this by slapping on a mutex.
Fixes: 13799748b957 ("powerpc/64: use interrupt restart table to speed up return from interrupt")
Cc: stable@vger.kernel.org # v5.14+
Signed-off-by: Russell Currey <ruscur@russell.cc>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211027072410.40950-1-ruscur@russell.cc
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
arch/powerpc/lib/feature-fixups.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index cda17bee5afe..c3e06922468b 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -228,6 +228,7 @@ static void do_stf_exit_barrier_fixups(enum stf_barrier_type types)
static bool stf_exit_reentrant = false;
static bool rfi_exit_reentrant = false;
+static DEFINE_MUTEX(exit_flush_lock);
static int __do_stf_barrier_fixups(void *data)
{
@@ -253,6 +254,9 @@ void do_stf_barrier_fixups(enum stf_barrier_type types)
* low level interrupt exit code before patching. After the patching,
* if allowed, then flip the branch to allow fast exits.
*/
+
+ // Prevent static key update races with do_rfi_flush_fixups()
+ mutex_lock(&exit_flush_lock);
static_branch_enable(&interrupt_exit_not_reentrant);
stop_machine(__do_stf_barrier_fixups, &types, NULL);
@@ -264,6 +268,8 @@ void do_stf_barrier_fixups(enum stf_barrier_type types)
if (stf_exit_reentrant && rfi_exit_reentrant)
static_branch_disable(&interrupt_exit_not_reentrant);
+
+ mutex_unlock(&exit_flush_lock);
}
void do_uaccess_flush_fixups(enum l1d_flush_type types)
@@ -486,6 +492,9 @@ void do_rfi_flush_fixups(enum l1d_flush_type types)
* without stop_machine, so this could be achieved with a broadcast
* IPI instead, but this matches the stf sequence.
*/
+
+ // Prevent static key update races with do_stf_barrier_fixups()
+ mutex_lock(&exit_flush_lock);
static_branch_enable(&interrupt_exit_not_reentrant);
stop_machine(__do_rfi_flush_fixups, &types, NULL);
@@ -497,6 +506,8 @@ void do_rfi_flush_fixups(enum l1d_flush_type types)
if (stf_exit_reentrant && rfi_exit_reentrant)
static_branch_disable(&interrupt_exit_not_reentrant);
+
+ mutex_unlock(&exit_flush_lock);
}
void do_barrier_nospec_fixups_range(bool enable, void *fixup_start, void *fixup_end)
--
2.26.2