Commit f6334f4a authored by John David Anglin's avatar John David Anglin Committed by Helge Deller
Browse files

parisc: Revise gateway LWS calls to probe user read access 



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: default avatarJohn David Anglin <dave.anglin@bell.net>
Signed-off-by: default avatarHelge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.12+
parent 4eab1c27

arch/parisc/kernel/syscall.S

+21 −9
Original line number Diff line number Diff line
@@ -613,6 +613,9 @@ 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 */
@@ -767,6 +770,9 @@ 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 */
@@ -951,41 +957,47 @@ 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)