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PING [PATCH v2] accel/tcg/user-exec: Fix read-modify-write of code on s3
From: |
Ilya Leoshkevich |
Subject: |
PING [PATCH v2] accel/tcg/user-exec: Fix read-modify-write of code on s390 hosts |
Date: |
Wed, 08 Sep 2021 14:16:13 +0200 |
User-agent: |
Evolution 3.38.4 (3.38.4-1.fc33) |
On Wed, 2021-08-04 at 00:16 +0200, Ilya Leoshkevich wrote:
> 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>
> ---
>
> v1:
> https://lists.nongnu.org/archive/html/qemu-devel/2021-08/msg00464.html
> v1 -> v2: Fix comment style, fix CSST detection (Richard).
>
> accel/tcg/user-exec.c | 48 ++++++++++++++++++++++++++++++++++++-----
> --
> 1 file changed, 41 insertions(+), 7 deletions(-)
>
> diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c
> index 90d1a2d327..8fed542622 100644
> --- a/accel/tcg/user-exec.c
> +++ b/accel/tcg/user-exec.c
> @@ -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);
> }
>
Hello,
Richard has reviewed this patch a while ago - is there anything else
that needs to be done before it can be picked up?
Best regards,
Ilya
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