[PATCH v2 0/2] target/s390x: Make PRNO TRNG interruptible

[PATCH v2 0/2] target/s390x: Make PRNO TRNG interruptible

[Ilya Leoshkevich]

v1: https://lore.kernel.org/qemu-devel/20260714113946.275122-1-iii@linux.ibm.com/
v1 -> v2: Use cpu_loop_exit_requested() (Richard).
          Apply R-b, since the change is trivial enough.


Hi,

Christian has reported that one can make a TCG guest stuck by running
PRNO TRNG with a huge buffer. This series fixes this by making PRNO
TRNG end on cpu_loop_exit_requested().

Patch 1 is the fix, patch 2 is the test.

Cc: Harald, because this may conflict with the CPACF series.

Best regards,
Ilya


Ilya Leoshkevich (2):
  target/s390x: Make PRNO TRNG interruptible
  tests/tcg/s390x: Test PRNO TRNG interruptibility

 target/s390x/tcg/crypto_helper.c | 22 ++++++++---
 tests/tcg/s390x/Makefile.target  |  1 +
 tests/tcg/s390x/prno-trng.c      | 67 ++++++++++++++++++++++++++++++++
 3 files changed, 85 insertions(+), 5 deletions(-)
 create mode 100644 tests/tcg/s390x/prno-trng.c

-- 
2.55.0

[PATCH v2 1/2] target/s390x: Make PRNO TRNG interruptible

[Ilya Leoshkevich]

fill_buf_random() writes the entire guest-requested amount of random
bytes in one go. Since the length is a full 64-bit value, a guest can
request several gigabytes and keep the vCPU spinning inside the helper,
without a chance to react to interrupts.

Do the same thing as HELPER(mvcl): check cpu_loop_exit_requested() at the
bottom of the loop, and when a return to the main loop is pending, stop
and report partial completion with condition code 3.

Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Fixes: 3dbc5fdacb5a ("target/s390x: support PRNO_TRNG instruction")
Cc: qemu-stable@nongnu.org
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 target/s390x/tcg/crypto_helper.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/target/s390x/tcg/crypto_helper.c b/target/s390x/tcg/crypto_helper.c
index 8fe0a222198..6a5dbe1cafa 100644
--- a/target/s390x/tcg/crypto_helper.c
+++ b/target/s390x/tcg/crypto_helper.c
@@ -16,6 +16,7 @@
 #include "qemu/guest-random.h"
 #include "s390x-internal.h"
 #include "tcg_s390x.h"
+#include "exec/cpu-common.h"
 #include "exec/helper-proto.h"
 #include "accel/tcg/cpu-ldst-common.h"
 #include "accel/tcg/cpu-mmu-index.h"
@@ -242,8 +243,8 @@ static int cpacf_sha512(CPUS390XState *env, const int mmu_idx, uintptr_t ra,
     return !len ? 0 : 3;
 }
 
-static void fill_buf_random(CPUS390XState *env, const int mmu_idx, uintptr_t ra,
-                            uint64_t *buf_reg, uint64_t *len_reg)
+static int fill_buf_random(CPUS390XState *env, const int mmu_idx, uintptr_t ra,
+                           uint64_t *buf_reg, uint64_t *len_reg)
 {
     const MemOpIdx oi = make_memop_idx(MO_8, mmu_idx);
     uint8_t tmp[256];
@@ -265,7 +266,13 @@ static void fill_buf_random(CPUS390XState *env, const int mmu_idx, uintptr_t ra,
             --*len_reg;
         }
         len -= block;
+
+        if (cpu_loop_exit_requested(env_cpu(env))) {
+            break;
+        }
     }
+
+    return len == 0 ? 0 : 3;
 }
 
 uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, uint32_t r2, uint32_t r3,
@@ -278,6 +285,7 @@ uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, uint32_t r2, uint32_t r3,
     uint8_t subfunc[16] = { 0 };
     uint64_t param_addr;
     MemOpIdx oi;
+    int cc;
 
     switch (type) {
     case S390_FEAT_TYPE_KMAC:
@@ -308,9 +316,13 @@ uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, uint32_t r2, uint32_t r3,
         return cpacf_sha512(env, mmu_idx, ra, env->regs[1], &env->regs[r2],
                             &env->regs[r2 + 1], type);
     case 114: /* CPACF_PRNO_TRNG */
-        fill_buf_random(env, mmu_idx, ra, &env->regs[r1], &env->regs[r1 + 1]);
-        fill_buf_random(env, mmu_idx, ra, &env->regs[r2], &env->regs[r2 + 1]);
-        break;
+        cc = fill_buf_random(env, mmu_idx, ra,
+                             &env->regs[r1], &env->regs[r1 + 1]);
+        if (cc == 0) {
+            cc = fill_buf_random(env, mmu_idx, ra,
+                                 &env->regs[r2], &env->regs[r2 + 1]);
+        }
+        return cc;
     default:
         /* we don't implement any other subfunction yet */
         g_assert_not_reached();
-- 
2.55.0

[PATCH v2 2/2] tests/tcg/s390x: Test PRNO TRNG interruptibility

[Ilya Leoshkevich]

Add a small test that issues a large PRNO TRNG request while a timer is
running, and checks that the timer interrupts it several times.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 tests/tcg/s390x/Makefile.target |  1 +
 tests/tcg/s390x/prno-trng.c     | 67 +++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)
 create mode 100644 tests/tcg/s390x/prno-trng.c

diff --git a/tests/tcg/s390x/Makefile.target b/tests/tcg/s390x/Makefile.target
index 0ca030ded01..48cba4cdfa4 100644
--- a/tests/tcg/s390x/Makefile.target
+++ b/tests/tcg/s390x/Makefile.target
@@ -75,6 +75,7 @@ Z13_TESTS+=vcksm
 Z13_TESTS+=vstl
 Z13_TESTS+=vrep
 Z13_TESTS+=precise-smc-user
+Z13_TESTS+=prno-trng
 $(Z13_TESTS): CFLAGS+=-march=z13 -O2
 TESTS+=$(Z13_TESTS)
 
diff --git a/tests/tcg/s390x/prno-trng.c b/tests/tcg/s390x/prno-trng.c
new file mode 100644
index 00000000000..43eea5db1dc
--- /dev/null
+++ b/tests/tcg/s390x/prno-trng.c
@@ -0,0 +1,67 @@
+/*
+ * Test that PERFORM RANDOM NUMBER OPERATION TRNG is interruptible.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include <assert.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/time.h>
+#include <asm/ucontext.h>
+
+static unsigned char buf1[16 * 1024 * 1024];
+static unsigned char buf2[16 * 1024 * 1024];
+
+static volatile sig_atomic_t interrupted;
+
+static void sigprof_handler(int sig, siginfo_t *info, void *ucontext)
+{
+    struct ucontext *uc = ucontext;
+    unsigned long addr = uc->uc_mcontext.regs.psw.addr;
+
+    if (*(unsigned short *)(addr - 4) == 0xb93c) {
+        interrupted++;
+    }
+}
+
+static void prno_trng(void *b1, unsigned long l1, void *b2, unsigned long l2)
+{
+    register unsigned long r0 asm("r0") = 114;  /* TRNG */
+    register unsigned long r2 asm("r2") = (unsigned long)b1;
+    register unsigned long r3 asm("r3") = l1;
+    register unsigned long r4 asm("r4") = (unsigned long)b2;
+    register unsigned long r5 asm("r5") = l2;
+
+    asm volatile("0: ppno %[r2],%[r4]\n"  /* prno alias for old toolchains */
+                 "   jo 0b"
+                 : [r2] "+r" (r2), [r3] "+r" (r3)
+                 , [r4] "+r" (r4), [r5] "+r" (r5)
+                 : "r" (r0)
+                 : "cc", "memory");
+}
+
+int main(void)
+{
+    struct itimerval it = {
+        .it_interval = { .tv_usec = 10000 },  /* 0.01s */
+        .it_value = { .tv_usec = 10000 },
+    };
+    struct sigaction act = {
+        .sa_sigaction = sigprof_handler,
+        .sa_flags = SA_SIGINFO,
+    };
+    int err;
+
+    err = sigaction(SIGPROF, &act, NULL);
+    assert(err == 0);
+    err = setitimer(ITIMER_PROF, &it, NULL);
+    assert(err == 0);
+
+    prno_trng(buf1, sizeof(buf1), buf2, sizeof(buf2));
+    printf("interrupted %d times\n", interrupted);
+    assert(interrupted >= 3);
+
+    return EXIT_SUCCESS;
+}
-- 
2.55.0

Re: [PATCH v2 1/2] target/s390x: Make PRNO TRNG interruptible

[Harald Freudenberger]

On 2026-07-14 21:17, Ilya Leoshkevich wrote:
> fill_buf_random() writes the entire guest-requested amount of random
> bytes in one go. Since the length is a full 64-bit value, a guest can
> request several gigabytes and keep the vCPU spinning inside the helper,
> without a chance to react to interrupts.
> 
> Do the same thing as HELPER(mvcl): check cpu_loop_exit_requested() at 
> the
> bottom of the loop, and when a return to the main loop is pending, stop
> and report partial completion with condition code 3.
> 
> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> Fixes: 3dbc5fdacb5a ("target/s390x: support PRNO_TRNG instruction")
> Cc: qemu-stable@nongnu.org
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  target/s390x/tcg/crypto_helper.c | 22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/target/s390x/tcg/crypto_helper.c 
> b/target/s390x/tcg/crypto_helper.c
> index 8fe0a222198..6a5dbe1cafa 100644
> --- a/target/s390x/tcg/crypto_helper.c
> +++ b/target/s390x/tcg/crypto_helper.c
> @@ -16,6 +16,7 @@
>  #include "qemu/guest-random.h"
>  #include "s390x-internal.h"
>  #include "tcg_s390x.h"
> +#include "exec/cpu-common.h"
>  #include "exec/helper-proto.h"
>  #include "accel/tcg/cpu-ldst-common.h"
>  #include "accel/tcg/cpu-mmu-index.h"
> @@ -242,8 +243,8 @@ static int cpacf_sha512(CPUS390XState *env, const
> int mmu_idx, uintptr_t ra,
>      return !len ? 0 : 3;
>  }
> 
> -static void fill_buf_random(CPUS390XState *env, const int mmu_idx,
> uintptr_t ra,
> -                            uint64_t *buf_reg, uint64_t *len_reg)
> +static int fill_buf_random(CPUS390XState *env, const int mmu_idx, 
> uintptr_t ra,
> +                           uint64_t *buf_reg, uint64_t *len_reg)
>  {
>      const MemOpIdx oi = make_memop_idx(MO_8, mmu_idx);
>      uint8_t tmp[256];
> @@ -265,7 +266,13 @@ static void fill_buf_random(CPUS390XState *env,
> const int mmu_idx, uintptr_t ra,
>              --*len_reg;
>          }
>          len -= block;
> +
> +        if (cpu_loop_exit_requested(env_cpu(env))) {
> +            break;
> +        }
>      }
> +
> +    return len == 0 ? 0 : 3;
>  }
> 
>  uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, uint32_t r2, 
> uint32_t r3,
> @@ -278,6 +285,7 @@ uint32_t HELPER(msa)(CPUS390XState *env, uint32_t
> r1, uint32_t r2, uint32_t r3,
>      uint8_t subfunc[16] = { 0 };
>      uint64_t param_addr;
>      MemOpIdx oi;
> +    int cc;
> 
>      switch (type) {
>      case S390_FEAT_TYPE_KMAC:
> @@ -308,9 +316,13 @@ uint32_t HELPER(msa)(CPUS390XState *env, uint32_t
> r1, uint32_t r2, uint32_t r3,
>          return cpacf_sha512(env, mmu_idx, ra, env->regs[1], 
> &env->regs[r2],
>                              &env->regs[r2 + 1], type);
>      case 114: /* CPACF_PRNO_TRNG */
> -        fill_buf_random(env, mmu_idx, ra, &env->regs[r1], 
> &env->regs[r1 + 1]);
> -        fill_buf_random(env, mmu_idx, ra, &env->regs[r2], 
> &env->regs[r2 + 1]);
> -        break;
> +        cc = fill_buf_random(env, mmu_idx, ra,
> +                             &env->regs[r1], &env->regs[r1 + 1]);
> +        if (cc == 0) {
> +            cc = fill_buf_random(env, mmu_idx, ra,
> +                                 &env->regs[r2], &env->regs[r2 + 1]);
> +        }
> +        return cc;
>      default:
>          /* we don't implement any other subfunction yet */
>          g_assert_not_reached();

Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>

Re: [PATCH v2 2/2] tests/tcg/s390x: Test PRNO TRNG interruptibility

[Harald Freudenberger]

On 2026-07-14 21:17, Ilya Leoshkevich wrote:
> Add a small test that issues a large PRNO TRNG request while a timer is
> running, and checks that the timer interrupts it several times.
> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  tests/tcg/s390x/Makefile.target |  1 +
>  tests/tcg/s390x/prno-trng.c     | 67 +++++++++++++++++++++++++++++++++
>  2 files changed, 68 insertions(+)
>  create mode 100644 tests/tcg/s390x/prno-trng.c
> 
> diff --git a/tests/tcg/s390x/Makefile.target 
> b/tests/tcg/s390x/Makefile.target
> index 0ca030ded01..48cba4cdfa4 100644
> --- a/tests/tcg/s390x/Makefile.target
> +++ b/tests/tcg/s390x/Makefile.target
> @@ -75,6 +75,7 @@ Z13_TESTS+=vcksm
>  Z13_TESTS+=vstl
>  Z13_TESTS+=vrep
>  Z13_TESTS+=precise-smc-user
> +Z13_TESTS+=prno-trng
>  $(Z13_TESTS): CFLAGS+=-march=z13 -O2
>  TESTS+=$(Z13_TESTS)
> 
> diff --git a/tests/tcg/s390x/prno-trng.c b/tests/tcg/s390x/prno-trng.c
> new file mode 100644
> index 00000000000..43eea5db1dc
> --- /dev/null
> +++ b/tests/tcg/s390x/prno-trng.c
> @@ -0,0 +1,67 @@
> +/*
> + * Test that PERFORM RANDOM NUMBER OPERATION TRNG is interruptible.
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +#include <assert.h>
> +#include <signal.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/time.h>
> +#include <asm/ucontext.h>
> +
> +static unsigned char buf1[16 * 1024 * 1024];
> +static unsigned char buf2[16 * 1024 * 1024];
> +
> +static volatile sig_atomic_t interrupted;
> +
> +static void sigprof_handler(int sig, siginfo_t *info, void *ucontext)
> +{
> +    struct ucontext *uc = ucontext;
> +    unsigned long addr = uc->uc_mcontext.regs.psw.addr;
> +
> +    if (*(unsigned short *)(addr - 4) == 0xb93c) {
> +        interrupted++;
> +    }
> +}
> +
> +static void prno_trng(void *b1, unsigned long l1, void *b2, unsigned 
> long l2)
> +{
> +    register unsigned long r0 asm("r0") = 114;  /* TRNG */
> +    register unsigned long r2 asm("r2") = (unsigned long)b1;
> +    register unsigned long r3 asm("r3") = l1;
> +    register unsigned long r4 asm("r4") = (unsigned long)b2;
> +    register unsigned long r5 asm("r5") = l2;
> +
> +    asm volatile("0: ppno %[r2],%[r4]\n"  /* prno alias for old 
> toolchains */
> +                 "   jo 0b"
> +                 : [r2] "+r" (r2), [r3] "+r" (r3)
> +                 , [r4] "+r" (r4), [r5] "+r" (r5)
> +                 : "r" (r0)
> +                 : "cc", "memory");
> +}
> +
> +int main(void)
> +{
> +    struct itimerval it = {
> +        .it_interval = { .tv_usec = 10000 },  /* 0.01s */
> +        .it_value = { .tv_usec = 10000 },
> +    };
> +    struct sigaction act = {
> +        .sa_sigaction = sigprof_handler,
> +        .sa_flags = SA_SIGINFO,
> +    };
> +    int err;
> +
> +    err = sigaction(SIGPROF, &act, NULL);
> +    assert(err == 0);
> +    err = setitimer(ITIMER_PROF, &it, NULL);
> +    assert(err == 0);
> +
> +    prno_trng(buf1, sizeof(buf1), buf2, sizeof(buf2));
> +    printf("interrupted %d times\n", interrupted);
> +    assert(interrupted >= 3);
> +
> +    return EXIT_SUCCESS;
> +}

Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>