[Stable-8.0.4 08/31] target/s390x: Fix MVCRL with a large value in R0

[Michael Tokarev]

From: Ilya Leoshkevich <iii@linux.ibm.com>

Using a large R0 causes an assertion error:

    qemu-s390x: target/s390x/tcg/mem_helper.c:183: access_prepare_nf: Assertion 
`size > 0 && size <= 4096' failed.

Even though PoP explicitly advises against using more than 8 bits for the
size, an emulator crash is never a good thing.

Fix by truncating the size to 8 bits.

Fixes: ea0a1053e276 ("s390x/tcg: Implement Miscellaneous-Instruction-Extensions 
Facility 3 for the s390x")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: qemu-stable@nongnu.org
Message-Id: <20230704081506.276055-5-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit 92a57534619a4058544ce8f9c0beae3e054f342b)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/target/s390x/tcg/mem_helper.c b/target/s390x/tcg/mem_helper.c
index 8b58b8d88d..7141d0ad88 100644
--- a/target/s390x/tcg/mem_helper.c
+++ b/target/s390x/tcg/mem_helper.c
@@ -514,6 +514,7 @@ void HELPER(mvcrl)(CPUS390XState *env, uint64_t l, uint64_t 
dest, uint64_t src)
     int32_t i;
 
     /* MVCRL always copies one more byte than specified - maximum is 256 */
+    l &= 0xff;
     l++;
 
     access_prepare(&srca, env, src, l, MMU_DATA_LOAD, mmu_idx, ra);
-- 
2.39.2