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parisc: Revise gateway LWS calls to probe user read access

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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>
This commit is contained in:
John David Anglin
2025-07-25 12:12:14 -04:00
committed by Greg Kroah-Hartman
parent 4c98107725
commit 8bccf47adb
1 changed files with 21 additions and 9 deletions
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30
arch/parisc/kernel/syscall.S
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@@ -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)