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[qemu-s390x] [PULL v2 10/34] s390x/tcg: Store only the necessary amount
From: |
Cornelia Huck |
Subject: |
[qemu-s390x] [PULL v2 10/34] s390x/tcg: Store only the necessary amount of doublewords for STFLE |
Date: |
Fri, 7 Jun 2019 16:17:03 +0200 |
From: David Hildenbrand <address@hidden>
The PoP (z14, 7-382) says:
Doublewords to the right of the doubleword in which the
highest-numbered facility bit is assigned for a model
may or may not be stored.
However, stack protection in certain binaries can't deal with that.
"gzip" example code:
f1b4: a7 08 00 03 lhi %r0,3
f1b8: b2 b0 f0 a0 stfle 160(%r15)
f1bc: e3 20 f0 b2 00 90 llgc %r2,178(%r15)
f1c2: c0 2b 00 00 00 01 nilf %r2,1
f1c8: b2 4f 00 10 ear %r1,%a0
f1cc: b9 14 00 22 lgfr %r2,%r2
f1d0: eb 11 00 20 00 0d sllg %r1,%r1,32
f1d6: b2 4f 00 11 ear %r1,%a1
f1da: d5 07 f0 b8 10 28 clc 184(8,%r15),40(%r1)
f1e0: a7 74 00 06 jne f1ec <file_read@@Base+0x1bc>
f1e4: eb ef f1 30 00 04 lmg %r14,%r15,304(%r15)
f1ea: 07 fe br %r14
f1ec: c0 e5 ff ff 9d 6e brasl %r14,2cc8 <__stack_chk_fail@plt>
In QEMU, we currently have:
max_bytes = 24
the code asks for (3 + 1) doublewords == 32 bytes.
If we write 32 bytes instead of only 24, and return "2 + 1" doublewords
("one less than the number of doulewords needed to contain all of the
facility bits"), the example code detects a stack corruption.
In my opinion, the code is wrong. However, it seems to work fine on
real machines. So let's limit storing to the minimum of the requested
and the maximum doublewords.
Cc: Stefan Liebler <address@hidden>
Cc: Andreas Krebbel <address@hidden>
Reviewed-by: Richard Henderson <address@hidden>
Signed-off-by: David Hildenbrand <address@hidden>
---
target/s390x/misc_helper.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/target/s390x/misc_helper.c b/target/s390x/misc_helper.c
index 34476134a407..10aa617cf9c5 100644
--- a/target/s390x/misc_helper.c
+++ b/target/s390x/misc_helper.c
@@ -678,7 +678,13 @@ uint32_t HELPER(stfle)(CPUS390XState *env, uint64_t addr)
prepare_stfl();
max_bytes = ROUND_UP(used_stfl_bytes, 8);
- for (i = 0; i < count_bytes; ++i) {
+
+ /*
+ * The PoP says that doublewords beyond the highest-numbered facility
+ * bit may or may not be stored. However, existing hardware appears to
+ * not store the words, and existing software depend on that.
+ */
+ for (i = 0; i < MIN(count_bytes, max_bytes); ++i) {
cpu_stb_data_ra(env, addr + i, stfl_bytes[i], ra);
}
--
2.20.1
- [qemu-s390x] [PULL v2 00/34] s390x updates, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 01/34] MAINTAINERS: cover tests/migration/s390x/, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 02/34] s390x/tcg: Implement VECTOR FIND ANY ELEMENT EQUAL, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 04/34] s390x/tcg: Implement VECTOR FIND ELEMENT NOT EQUAL, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 03/34] s390x/tcg: Implement VECTOR FIND ELEMENT EQUAL, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 05/34] s390x/tcg: Implement VECTOR ISOLATE STRING, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 06/34] s390x/tcg: Implement VECTOR STRING RANGE COMPARE, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 07/34] s390x: Align vector registers to 16 bytes, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 10/34] s390x/tcg: Store only the necessary amount of doublewords for STFLE,
Cornelia Huck <=
- [qemu-s390x] [PULL v2 09/34] s390x/tcg: Fix max_byte detection for stfle, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 11/34] s390x/tcg: Introduce tcg_s390_vector_exception(), Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 08/34] s390x: Use uint64_t for vector registers, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 12/34] s390x/tcg: Export float_comp_to_cc() and float(32|64|128)_dcmask(), Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 14/34] s390x/tcg: Implement VECTOR FP COMPARE (AND SIGNAL) SCALAR, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 13/34] s390x/tcg: Implement VECTOR FP ADD, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 15/34] s390x/tcg: Implement VECTOR FP COMPARE (EQUAL|HIGH|HIGH OR EQUAL), Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 16/34] s390x/tcg: Implement VECTOR FP CONVERT FROM FIXED 64-BIT, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 17/34] s390x/tcg: Implement VECTOR FP CONVERT FROM LOGICAL 64-BIT, Cornelia Huck, 2019/06/07
- [qemu-s390x] [PULL v2 18/34] s390x/tcg: Implement VECTOR FP CONVERT TO FIXED 64-BIT, Cornelia Huck, 2019/06/07