Re: [PATCH 6/6] arm64: trap userspace "dc cvau" cache operation on errata-affected core

From: Suzuki K Poulose
Date: Tue Jun 14 2016 - 12:16:57 EST


On 09/05/16 17:49, Andre Przywara wrote:
The ARM errata 819472, 826319, 827319 and 824069 for affected
Cortex-A53 cores demand to promote "dc cvau" instructions to
"dc civac". Since we allow userspace to also emit those instructions,
we should make sure that "dc cvau" gets promoted there too.
So lets grasp the nettle here and actually trap every userland cache
maintenance instruction once we detect at least one affected core in
the system.
We then emulate the instruction by executing it on behalf of userland,
promoting "dc cvau" to "dc civac" on the way and injecting access
fault back into userspace.

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>


+
+asmlinkage void __exception do_sysinstr(unsigned int esr, struct pt_regs *regs)
+{
+ unsigned long address;
+ int ret;
+
+ /* if this is a write with: Op0=1, Op2=1, Op1=3, CRn=7 */
+ if ((esr & 0x01fffc01) == 0x0012dc00) {
+ int rt = (esr >> 5) & 0x1f;
+ int crm = (esr >> 1) & 0x0f;
+
+ address = regs->regs[rt];
+
+ switch (crm) {
+ case 11: /* DC CVAU, gets promoted */
+ __user_cache_maint("dc civac", address, ret);
+ break;
+ case 10: /* DC CVAC, gets promoted */
+ __user_cache_maint("dc civac", address, ret);
+ break;
+ case 14: /* DC CIVAC */
+ __user_cache_maint("dc civac", address, ret);
+ break;
+ case 5: /* IC IVAU */
+ __user_cache_maint("ic ivau", address, ret);
+ break;
+ default:
+ force_signal_inject(SIGILL, ILL_ILLOPC, regs, 0);
+ return;
+ }
+ } else {
+ force_signal_inject(SIGILL, ILL_ILLOPC, regs, 0);
+ return;

Correct me if I am wrong, I think we should handle DC ZVA and emulate the same ?
Thats the only EL0 accessible instruction we don't handle above.

Suzuki