Re: [PATCH v2 06/41] linux-user: Reorg handling for SIGSEGV

[Alistair Francis]

On Sun, Sep 19, 2021 at 4:55 AM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Add stub host-signal.h for all linux-user hosts.
> Add new code replacing cpu_signal_handler.
> Full migration will happen one host at a time.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Acked-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  linux-user/host/aarch64/host-signal.h |   1 +
>  linux-user/host/arm/host-signal.h     |   1 +
>  linux-user/host/i386/host-signal.h    |   1 +
>  linux-user/host/mips/host-signal.h    |   1 +
>  linux-user/host/ppc/host-signal.h     |   1 +
>  linux-user/host/ppc64/host-signal.h   |   1 +
>  linux-user/host/riscv/host-signal.h   |   1 +
>  linux-user/host/s390/host-signal.h    |   1 +
>  linux-user/host/s390x/host-signal.h   |   1 +
>  linux-user/host/sparc/host-signal.h   |   1 +
>  linux-user/host/sparc64/host-signal.h |   1 +
>  linux-user/host/x32/host-signal.h     |   1 +
>  linux-user/host/x86_64/host-signal.h  |   1 +
>  linux-user/signal.c                   | 109 ++++++++++++++++++++++----
>  14 files changed, 106 insertions(+), 16 deletions(-)
>  create mode 100644 linux-user/host/aarch64/host-signal.h
>  create mode 100644 linux-user/host/arm/host-signal.h
>  create mode 100644 linux-user/host/i386/host-signal.h
>  create mode 100644 linux-user/host/mips/host-signal.h
>  create mode 100644 linux-user/host/ppc/host-signal.h
>  create mode 100644 linux-user/host/ppc64/host-signal.h
>  create mode 100644 linux-user/host/riscv/host-signal.h
>  create mode 100644 linux-user/host/s390/host-signal.h
>  create mode 100644 linux-user/host/s390x/host-signal.h
>  create mode 100644 linux-user/host/sparc/host-signal.h
>  create mode 100644 linux-user/host/sparc64/host-signal.h
>  create mode 100644 linux-user/host/x32/host-signal.h
>  create mode 100644 linux-user/host/x86_64/host-signal.h
>
> diff --git a/linux-user/host/aarch64/host-signal.h 
> b/linux-user/host/aarch64/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/aarch64/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/arm/host-signal.h 
> b/linux-user/host/arm/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/arm/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/i386/host-signal.h 
> b/linux-user/host/i386/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/i386/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/mips/host-signal.h 
> b/linux-user/host/mips/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/mips/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/ppc/host-signal.h 
> b/linux-user/host/ppc/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/ppc/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/ppc64/host-signal.h 
> b/linux-user/host/ppc64/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/ppc64/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/riscv/host-signal.h 
> b/linux-user/host/riscv/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/riscv/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/s390/host-signal.h 
> b/linux-user/host/s390/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/s390/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/s390x/host-signal.h 
> b/linux-user/host/s390x/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/s390x/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/sparc/host-signal.h 
> b/linux-user/host/sparc/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/sparc/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/sparc64/host-signal.h 
> b/linux-user/host/sparc64/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/sparc64/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/x32/host-signal.h 
> b/linux-user/host/x32/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/x32/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/host/x86_64/host-signal.h 
> b/linux-user/host/x86_64/host-signal.h
> new file mode 100644
> index 0000000000..f4b4d65031
> --- /dev/null
> +++ b/linux-user/host/x86_64/host-signal.h
> @@ -0,0 +1 @@
> +#define HOST_SIGNAL_PLACEHOLDER
> diff --git a/linux-user/signal.c b/linux-user/signal.c
> index 5ea8e4584a..6f953f10d4 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -18,12 +18,15 @@
>   */
>  #include "qemu/osdep.h"
>  #include "qemu/bitops.h"
> +#include "hw/core/tcg-cpu-ops.h"
> +
>  #include <sys/ucontext.h>
>  #include <sys/resource.h>
>
>  #include "qemu.h"
>  #include "trace.h"
>  #include "signal-common.h"
> +#include "host-signal.h"
>
>  static struct target_sigaction sigact_table[TARGET_NSIG];
>
> @@ -761,41 +764,115 @@ static inline void rewind_if_in_safe_syscall(void *puc)
>  }
>  #endif
>
> -static void host_signal_handler(int host_signum, siginfo_t *info,
> -                                void *puc)
> +static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
>  {
>      CPUArchState *env = thread_cpu->env_ptr;
>      CPUState *cpu = env_cpu(env);
>      TaskState *ts = cpu->opaque;
> -
> -    int sig;
>      target_siginfo_t tinfo;
>      ucontext_t *uc = puc;
>      struct emulated_sigtable *k;
> +    int guest_sig;
>
> +#ifdef HOST_SIGNAL_PLACEHOLDER
>      /* the CPU emulator uses some host signals to detect exceptions,
>         we forward to it some signals */
> -    if ((host_signum == SIGSEGV || host_signum == SIGBUS)
> +    if ((host_sig == SIGSEGV || host_sig == SIGBUS)
>          && info->si_code > 0) {
> -        if (cpu_signal_handler(host_signum, info, puc))
> +        if (cpu_signal_handler(host_sig, info, puc))
>              return;
>      }
> +#else
> +    uintptr_t pc = 0;
> +    bool sync_sig = false;
> +
> +    /*
> +     * Non-spoofed SIGSEGV and SIGBUS are synchronous, and need special
> +     * handling wrt signal blocking and unwinding.
> +     */
> +    if ((host_sig == SIGSEGV || host_sig == SIGBUS) && info->si_code > 0) {
> +        MMUAccessType access_type;
> +        uintptr_t host_addr;
> +        abi_ptr guest_addr;
> +        bool is_write;
> +
> +        host_addr = (uintptr_t)info->si_addr;
> +
> +        /*
> +         * Convert forcefully to guest address space: addresses outside
> +         * reserved_va are still valid to report via SEGV_MAPERR.
> +         */
> +        guest_addr = h2g_nocheck(host_addr);
> +
> +        pc = host_signal_pc(uc);
> +        is_write = host_signal_write(info, uc);
> +        access_type = adjust_signal_pc(&pc, is_write);
> +
> +        if (host_sig == SIGSEGV) {
> +            const struct TCGCPUOps *tcg_ops;
> +
> +            if (info->si_code == SEGV_ACCERR && h2g_valid(host_addr)) {
> +                /* If this was a write to a TB protected page, restart. */
> +                if (is_write &&
> +                    handle_sigsegv_accerr_write(cpu, &uc->uc_sigmask,
> +                                                pc, guest_addr)) {
> +                    return;
> +                }
> +
> +                /*
> +                 * With reserved_va, the whole address space is PROT_NONE,
> +                 * which means that we may get ACCERR when we want MAPERR.
> +                 */
> +                if (page_get_flags(guest_addr) & PAGE_VALID) {
> +                    /* maperr = false; */
> +                } else {
> +                    info->si_code = SEGV_MAPERR;
> +                }
> +            }
> +
> +            sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
> +
> +            tcg_ops = CPU_GET_CLASS(cpu)->tcg_ops;
> +            tcg_ops->tlb_fill(cpu, guest_addr, 0, access_type,
> +                              MMU_USER_IDX, false, pc);
> +            g_assert_not_reached();
> +        } else {
> +            sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
> +        }
> +
> +        sync_sig = true;
> +    }
> +#endif
>
>      /* get target signal number */
> -    sig = host_to_target_signal(host_signum);
> -    if (sig < 1 || sig > TARGET_NSIG)
> +    guest_sig = host_to_target_signal(host_sig);
> +    if (guest_sig < 1 || guest_sig > TARGET_NSIG) {
>          return;
> -    trace_user_host_signal(env, host_signum, sig);
> +    }
> +    trace_user_host_signal(env, host_sig, guest_sig);
> +
> +    host_to_target_siginfo_noswap(&tinfo, info);
> +    k = &ts->sigtab[guest_sig - 1];
> +    k->info = tinfo;
> +    k->pending = guest_sig;
> +    ts->signal_pending = 1;
> +
> +#ifndef HOST_SIGNAL_PLACEHOLDER
> +    /*
> +     * For synchronous signals, unwind the cpu state to the faulting
> +     * insn and then exit back to the main loop so that the signal
> +     * is delivered immediately.
> +     */
> +    if (sync_sig) {
> +        cpu->exception_index = EXCP_INTERRUPT;
> +        cpu_loop_exit_restore(cpu, pc);
> +    }
> +#endif
>
>      rewind_if_in_safe_syscall(puc);
>
> -    host_to_target_siginfo_noswap(&tinfo, info);
> -    k = &ts->sigtab[sig - 1];
> -    k->info = tinfo;
> -    k->pending = sig;
> -    ts->signal_pending = 1;
> -
> -    /* Block host signals until target signal handler entered. We
> +    /*
> +     * Block host signals until target signal handler entered. We
>       * can't block SIGSEGV or SIGBUS while we're executing guest
>       * code in case the guest code provokes one in the window between
>       * now and it getting out to the main loop. Signals will be
> --
> 2.25.1
>
>