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authorRussell Currey <ruscur@russell.cc>2021-10-27 10:24:10 +0300
committerMichael Ellerman <mpe@ellerman.id.au>2021-10-28 09:23:58 +0300
commit3c12b4df8d5e026345a19886ae375b3ebc33c0b6 (patch)
tree4539f57d2e176ac8f1473bb38a05cd3d1ad3e137 /arch/powerpc/lib
parent5d354dc35ebb0b224d627264c60f60dbda3a1bc3 (diff)
downloadlinux-3c12b4df8d5e026345a19886ae375b3ebc33c0b6.tar.xz
powerpc/security: Use a mutex for interrupt exit code patching
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
Diffstat (limited to 'arch/powerpc/lib')
-rw-r--r--arch/powerpc/lib/feature-fixups.c11
1 files changed, 11 insertions, 0 deletions
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)