powerpc/64e: Fix early TLB miss with KUAP

With KUAP, the TLB miss handler bails out when an access to user
memory is performed with a nul TID.

But the normal TLB miss routine which is only used early during boot
does the check regardless for all memory areas, not only user memory.

By chance there is no early IO or vmalloc access, but when KASAN
come we will start having early TLB misses.

Fix it by creating a special branch for user accesses similar to the
one in the 'bolted' TLB miss handlers. Unfortunately SPRN_MAS1 is
now read too early and there are no registers available to preserve
it so it will be read a second time.

Fixes: 57bc963837f5 ("powerpc/kuap: Wire-up KUAP on book3e/64")
Cc: stable@vger.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/8d6c5859a45935d6e1a336da4dc20be421e8cea7.1656427701.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/mm/nohash/tlb_low_64e.S b/arch/powerpc/mm/nohash/tlb_low_64e.S
index 8b97c4acfebfa2d373bc50a4f8f32c5bd4ae9d9c..9e9ab3803fb2ffc78bcce5cb0b5ebc14e1d224dd 100644 (file)
--- a/arch/powerpc/mm/nohash/tlb_low_64e.S
+++ b/arch/powerpc/mm/nohash/tlb_low_64e.S
@@ -583,7 +583,7 @@ itlb_miss_fault_e6500:
         */
        rlwimi  r11,r14,32-19,27,27
        rlwimi  r11,r14,32-16,19,19
-       beq     normal_tlb_miss
+       beq     normal_tlb_miss_user
        /* XXX replace the RMW cycles with immediate loads + writes */
 1:     mfspr   r10,SPRN_MAS1
        cmpldi  cr0,r15,8               /* Check for vmalloc region */
@@ -626,7 +626,7 @@ itlb_miss_fault_e6500:
 
        cmpldi  cr0,r15,0                       /* Check for user region */
        std     r14,EX_TLB_ESR(r12)             /* write crazy -1 to frame */
-       beq     normal_tlb_miss
+       beq     normal_tlb_miss_user
 
        li      r11,_PAGE_PRESENT|_PAGE_BAP_SX  /* Base perm */
        oris    r11,r11,_PAGE_ACCESSED@h
@@ -653,6 +653,12 @@ itlb_miss_fault_e6500:
  * r11 = PTE permission mask
  * r10 = crap (free to use)
  */
+normal_tlb_miss_user:
+#ifdef CONFIG_PPC_KUAP
+       mfspr   r14,SPRN_MAS1
+       rlwinm. r14,r14,0,0x3fff0000
+       beq-    normal_tlb_miss_access_fault /* KUAP fault */
+#endif
 normal_tlb_miss:
        /* So we first construct the page table address. We do that by
         * shifting the bottom of the address (not the region ID) by
@@ -683,11 +689,6 @@ finish_normal_tlb_miss:
        /* Check if required permissions are met */
        andc.   r15,r11,r14
        bne-    normal_tlb_miss_access_fault
-#ifdef CONFIG_PPC_KUAP
-       mfspr   r11,SPRN_MAS1
-       rlwinm. r10,r11,0,0x3fff0000
-       beq-    normal_tlb_miss_access_fault /* KUAP fault */
-#endif
 
        /* Now we build the MAS:
         *
@@ -709,9 +710,7 @@ finish_normal_tlb_miss:
        rldicl  r10,r14,64-8,64-8
        cmpldi  cr0,r10,BOOK3E_PAGESZ_4K
        beq-    1f
-#ifndef CONFIG_PPC_KUAP
        mfspr   r11,SPRN_MAS1
-#endif
        rlwimi  r11,r14,31,21,24
        rlwinm  r11,r11,0,21,19
        mtspr   SPRN_MAS1,r11