parisc: Revise gateway LWS calls to probe user read access

commit f6334f4ae9a4e962ba74b026e1d965dfdf8cbef8 upstream.

We use load and stbys,e instructions to trigger memory reference
interruptions without writing to memory. Because of the way read
access support is implemented, read access interruptions are only
triggered at privilege levels 2 and 3. The kernel and gateway
page execute at privilege level 0, so this code never triggers
a read access interruption. Thus, it is currently possible for
user code to execute a LWS compare and swap operation at an
address that is read protected at privilege level 3 (PRIV_USER).

Fix this by probing read access rights at privilege level 3 and
branching to lws_fault if access isn't allowed.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.12+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
index f0f49ca703624afc3e4a72f4c1d46c33dc8d055c..670aed0dea370fc9635dbccfa4c1502f422386f2 100644 (file)
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -600,6 +600,9 @@ lws_compare_and_swap32:
 lws_compare_and_swap:
        /* Trigger memory reference interruptions without writing to memory */
 1:     ldw     0(%r26), %r28
+       proberi (%r26), PRIV_USER, %r28
+       comb,=,n        %r28, %r0, lws_fault /* backwards, likely not taken */
+       nop
 2:     stbys,e %r0, 0(%r26)
 
        /* Calculate 8-bit hash index from virtual address */
@@ -753,6 +756,9 @@ cas2_lock_start:
        copy    %r26, %r28
        depi_safe       0, 31, 2, %r28
 10:    ldw     0(%r28), %r1
+       proberi (%r28), PRIV_USER, %r1
+       comb,=,n        %r1, %r0, lws_fault /* backwards, likely not taken */
+       nop
 11:    stbys,e %r0, 0(%r28)
 
        /* Calculate 8-bit hash index from virtual address */
@@ -936,41 +942,47 @@ atomic_xchg_begin:
 
        /* 8-bit exchange */
 1:     ldb     0(%r24), %r20
+       proberi (%r24), PRIV_USER, %r20
+       comb,=,n        %r20, %r0, lws_fault /* backwards, likely not taken */
+       nop
        copy    %r23, %r20
        depi_safe       0, 31, 2, %r20
        b       atomic_xchg_start
 2:     stbys,e %r0, 0(%r20)
-       nop
-       nop
-       nop
 
        /* 16-bit exchange */
 3:     ldh     0(%r24), %r20
+       proberi (%r24), PRIV_USER, %r20
+       comb,=,n        %r20, %r0, lws_fault /* backwards, likely not taken */
+       nop
        copy    %r23, %r20
        depi_safe       0, 31, 2, %r20
        b       atomic_xchg_start
 4:     stbys,e %r0, 0(%r20)
-       nop
-       nop
-       nop
 
        /* 32-bit exchange */
 5:     ldw     0(%r24), %r20
+       proberi (%r24), PRIV_USER, %r20
+       comb,=,n        %r20, %r0, lws_fault /* backwards, likely not taken */
+       nop
        b       atomic_xchg_start
 6:     stbys,e %r0, 0(%r23)
        nop
        nop
-       nop
-       nop
-       nop
 
        /* 64-bit exchange */
 #ifdef CONFIG_64BIT
 7:     ldd     0(%r24), %r20
+       proberi (%r24), PRIV_USER, %r20
+       comb,=,n        %r20, %r0, lws_fault /* backwards, likely not taken */
+       nop
 8:     stdby,e %r0, 0(%r23)
 #else
 7:     ldw     0(%r24), %r20
 8:     ldw     4(%r24), %r20
+       proberi (%r24), PRIV_USER, %r20
+       comb,=,n        %r20, %r0, lws_fault /* backwards, likely not taken */
+       nop
        copy    %r23, %r20
        depi_safe       0, 31, 2, %r20
 9:     stbys,e %r0, 0(%r20)