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accel/tcg/user-exec: Fix read-modify-write of code on s390 hosts

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x86_64 dotnet/runtime uses cmpxchg for code patching. When running it
under s390x qemu-linux user, cpu_signal_handler() does not recognize
this as a write and does not restore PAGE_WRITE cleared by
tb_page_add(), incorrectly forwarding the signal to the guest code.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210803221606.150103-1-iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Ilya Leoshkevich 2021-08-04 00:16:06 +02:00 committed by Richard Henderson
parent 76d0042bb2
commit db17d2cdb1
1 changed files with 41 additions and 7 deletions
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48
accel/tcg/user-exec.c
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@ -680,18 +680,26 @@ int cpu_signal_handler(int host_signum, void *pinfo,
pc = uc->uc_mcontext.psw.addr;
/* ??? On linux, the non-rt signal handler has 4 (!) arguments instead
of the normal 2 arguments. The 3rd argument contains the "int_code"
from the hardware which does in fact contain the is_write value.
The rt signal handler, as far as I can tell, does not give this value
at all. Not that we could get to it from here even if it were. */
/* ??? This is not even close to complete, since it ignores all
of the read-modify-write instructions. */
/*
* ??? On linux, the non-rt signal handler has 4 (!) arguments instead
* of the normal 2 arguments. The 4th argument contains the "Translation-
* Exception Identification for DAT Exceptions" from the hardware (aka
* "int_parm_long"), which does in fact contain the is_write value.
* The rt signal handler, as far as I can tell, does not give this value
* at all. Not that we could get to it from here even if it were.
* So fall back to parsing instructions. Treat read-modify-write ones as
* writes, which is not fully correct, but for tracking self-modifying code
* this is better than treating them as reads. Checking si_addr page flags
* might be a viable improvement, albeit a racy one.
*/
/* ??? This is not even close to complete. */
pinsn = (uint16_t *)pc;
switch (pinsn[0] >> 8) {
case 0x50: /* ST */
case 0x42: /* STC */
case 0x40: /* STH */
case 0xba: /* CS */
case 0xbb: /* CDS */
is_write = 1;
break;
case 0xc4: /* RIL format insns */
@ -702,6 +710,12 @@ int cpu_signal_handler(int host_signum, void *pinfo,
is_write = 1;
}
break;
case 0xc8: /* SSF format insns */
switch (pinsn[0] & 0xf) {
case 0x2: /* CSST */
is_write = 1;
}
break;
case 0xe3: /* RXY format insns */
switch (pinsn[2] & 0xff) {
case 0x50: /* STY */
@ -715,7 +729,27 @@ int cpu_signal_handler(int host_signum, void *pinfo,
is_write = 1;
}
break;
case 0xeb: /* RSY format insns */
switch (pinsn[2] & 0xff) {
case 0x14: /* CSY */
case 0x30: /* CSG */
case 0x31: /* CDSY */
case 0x3e: /* CDSG */
case 0xe4: /* LANG */
case 0xe6: /* LAOG */
case 0xe7: /* LAXG */
case 0xe8: /* LAAG */
case 0xea: /* LAALG */
case 0xf4: /* LAN */
case 0xf6: /* LAO */
case 0xf7: /* LAX */
case 0xfa: /* LAAL */
case 0xf8: /* LAA */
is_write = 1;
}
break;
}
return handle_cpu_signal(pc, info, is_write, &uc->uc_sigmask);
}