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powerpc/security: Use a mutex for interrupt exit code patching

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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: 13799748b9 ("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
This commit is contained in:
Russell Currey 2021-10-27 17:24:10 +10:00 committed by Michael Ellerman
parent 5d354dc35e
commit 3c12b4df8d
1 changed files with 11 additions and 0 deletions
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11
arch/powerpc/lib/feature-fixups.c
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@ -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)