| Message ID | 20210506044959.1298123-1-mpe@ellerman.id.au (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [v2,1/2] powerpc/64s: Fix crashes when toggling stf barrier | expand |
| Related | show |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/apply_patch | success | Successfully applied on branch powerpc/merge (7619d98e5041d5c25aba5428704dba6121237a9a) |
| snowpatch_ozlabs/checkpatch | warning | total: 0 errors, 1 warnings, 0 checks, 34 lines checked |
| snowpatch_ozlabs/needsstable | success | Patch is tagged for stable |
On Thu, 6 May 2021 14:49:58 +1000, Michael Ellerman wrote: > The STF (store-to-load forwarding) barrier mitigation can be > enabled/disabled at runtime via a debugfs file (stf_barrier), which > causes the kernel to patch itself to enable/disable the relevant > mitigations. > > However depending on which mitigation we're using, it may not be safe to > do that patching while other CPUs are active. For example the following > crash: > > [...] Applied to powerpc/fixes. [1/2] powerpc/64s: Fix crashes when toggling stf barrier https://git.kernel.org/powerpc/c/8ec7791bae1327b1c279c5cd6e929c3b12daaf0a [2/2] powerpc/64s: Fix crashes when toggling entry flush barrier https://git.kernel.org/powerpc/c/aec86b052df6541cc97c5fca44e5934cbea4963b cheers
diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c index 1fd31b4b0e13..10083add8b33 100644 --- a/arch/powerpc/lib/feature-fixups.c +++ b/arch/powerpc/lib/feature-fixups.c @@ -14,6 +14,7 @@ #include <linux/string.h> #include <linux/init.h> #include <linux/sched/mm.h> +#include <linux/stop_machine.h> #include <asm/cputable.h> #include <asm/code-patching.h> #include <asm/page.h> @@ -227,11 +228,25 @@ static void do_stf_exit_barrier_fixups(enum stf_barrier_type types) : "unknown"); } +static int __do_stf_barrier_fixups(void *data) +{ + enum stf_barrier_type *types = data; + + do_stf_entry_barrier_fixups(*types); + do_stf_exit_barrier_fixups(*types); + + return 0; +} void do_stf_barrier_fixups(enum stf_barrier_type types) { - do_stf_entry_barrier_fixups(types); - do_stf_exit_barrier_fixups(types); + /* + * The call to the fallback entry flush, and the fallback/sync-ori exit + * flush can not be safely patched in/out while other CPUs are executing + * them. So call __do_stf_barrier_fixups() on one CPU while all other CPUs + * spin in the stop machine core with interrupts hard disabled. + */ + stop_machine(__do_stf_barrier_fixups, &types, NULL); } void do_uaccess_flush_fixups(enum l1d_flush_type types)
The STF (store-to-load forwarding) barrier mitigation can be enabled/disabled at runtime via a debugfs file (stf_barrier), which causes the kernel to patch itself to enable/disable the relevant mitigations. However depending on which mitigation we're using, it may not be safe to do that patching while other CPUs are active. For example the following crash: User access of kernel address (c00000003fff5af0) - exploit attempt? (uid: 0) segfault (11) at c00000003fff5af0 nip 7fff8ad12198 lr 7fff8ad121f8 code 1 code: 40820128 e93c00d0 e9290058 7c292840 40810058 38600000 4bfd9a81 e8410018 code: 2c030006 41810154 3860ffb6 e9210098 <e94d8ff0> 7d295279 39400000 40820a3c Shows that we returned to userspace without restoring the user r13 value, due to executing the partially patched STF exit code. Fix it by doing the patching under stop machine. The CPUs that aren't doing the patching will be spinning in the core of the stop machine logic. That is currently sufficient for our purposes, because none of the patching we do is to that code or anywhere in the vicinity. Fixes: a048a07d7f45 ("powerpc/64s: Add support for a store forwarding barrier at kernel entry/exit") Cc: stable@vger.kernel.org # v4.17+ Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> --- arch/powerpc/lib/feature-fixups.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) v2: Fix the bugs. Pass a pointer to types, rather than wedging into the void *. Use stop_machine().