Le 25/07/2019 à 15:16, Peter Maydell a écrit :
> The alternate signal stack set up by the sigaltstack syscall is
> supposed to be per-thread. We were incorrectly implementing it as
> process-wide. This causes problems for guest binaries that rely on
> this. Notably the Go runtime does, and so we were seeing crashes
> caused by races where two guest threads might incorrectly both
> execute on the same stack simultaneously.
>
> Replace the global target_sigaltstack_used with a field
> sigaltstack_used in the TaskState, and make all the references to the
> old global instead get a pointer to the TaskState and use the field.
>
> Fixes: https://bugs.launchpad.net/qemu/+bug/1696773
> Signed-off-by: Peter Maydell
> ---
> I've marked this as "for-4.1" but it is quite late in the release
> cycle and I think this could use more testing than I have given it...
It looks good. I'm going to test it with LTP on all the targets I have.
I will test the go program too.
Thanks,
Laurent
>
> Thanks are due to:
> * the original bug reporter, for providing a nice simple test case
> * rr, for allowing me to capture and forensically examine a single
>example of the failure
> * the Go project for having a good clear HACKING.md that explained
>their stack usage and mentioned specifically that signal stacks
>are per-thread (per-M, in their terms)
> * a colleague, for prodding me into actually spending the necessary
>two days grovelling through gdb sessions and logs to figure out
>what was actually going wrong
> ---
> linux-user/qemu.h | 2 ++
> linux-user/signal-common.h | 1 -
> linux-user/hppa/signal.c | 3 ++-
> linux-user/main.c | 5 +
> linux-user/signal.c| 35 +++
> 5 files changed, 28 insertions(+), 18 deletions(-)
>
> diff --git a/linux-user/qemu.h b/linux-user/qemu.h
> index 4258e4162d2..aac03346270 100644
> --- a/linux-user/qemu.h
> +++ b/linux-user/qemu.h
> @@ -151,6 +151,8 @@ typedef struct TaskState {
> */
> int signal_pending;
>
> +/* This thread's sigaltstack, if it has one */
> +struct target_sigaltstack sigaltstack_used;
> } __attribute__((aligned(16))) TaskState;
>
> extern char *exec_path;
> diff --git a/linux-user/signal-common.h b/linux-user/signal-common.h
> index 51030a93069..1df1068552f 100644
> --- a/linux-user/signal-common.h
> +++ b/linux-user/signal-common.h
> @@ -19,7 +19,6 @@
>
> #ifndef SIGNAL_COMMON_H
> #define SIGNAL_COMMON_H
> -extern struct target_sigaltstack target_sigaltstack_used;
>
> int on_sig_stack(unsigned long sp);
> int sas_ss_flags(unsigned long sp);
> diff --git a/linux-user/hppa/signal.c b/linux-user/hppa/signal.c
> index b6927ee6735..d1a58feeb36 100644
> --- a/linux-user/hppa/signal.c
> +++ b/linux-user/hppa/signal.c
> @@ -111,10 +111,11 @@ void setup_rt_frame(int sig, struct target_sigaction
> *ka,
> abi_ulong frame_addr, sp, haddr;
> struct target_rt_sigframe *frame;
> int i;
> +TaskState *ts = (TaskState *)thread_cpu->opaque;
>
> sp = get_sp_from_cpustate(env);
> if ((ka->sa_flags & TARGET_SA_ONSTACK) && !sas_ss_flags(sp)) {
> -sp = (target_sigaltstack_used.ss_sp + 0x7f) & ~0x3f;
> +sp = (ts->sigaltstack_used.ss_sp + 0x7f) & ~0x3f;
> }
> frame_addr = QEMU_ALIGN_UP(sp, 64);
> sp = frame_addr + PARISC_RT_SIGFRAME_SIZE32;
> diff --git a/linux-user/main.c b/linux-user/main.c
> index a59ae9439de..8ffc5251955 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -180,6 +180,11 @@ void stop_all_tasks(void)
> void init_task_state(TaskState *ts)
> {
> ts->used = 1;
> +ts->sigaltstack_used = (struct target_sigaltstack) {
> +.ss_sp = 0,
> +.ss_size = 0,
> +.ss_flags = TARGET_SS_DISABLE,
> +};
> }
>
> CPUArchState *cpu_copy(CPUArchState *env)
> diff --git a/linux-user/signal.c b/linux-user/signal.c
> index 5cd237834d9..5ca6d62b15d 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -25,12 +25,6 @@
> #include "trace.h"
> #include "signal-common.h"
>
> -struct target_sigaltstack target_sigaltstack_used = {
> -.ss_sp = 0,
> -.ss_size = 0,
> -.ss_flags = TARGET_SS_DISABLE,
> -};
> -
> static struct target_sigaction sigact_table[TARGET_NSIG];
>
> static void host_signal_handler(int host_signum, siginfo_t *info,
> @@ -251,13 +245,17 @@ void set_sigmask(const sigset_t *set)
>
> int on_sig_stack(unsigned long sp)
> {
> -return (sp - target_sigaltstack_used.ss_sp
> -< target_sigaltstack_used.ss_size);
> +TaskState *ts = (TaskState *)thread_cpu->opaque;
> +
> +return (sp - ts->sigaltstack_used.ss_sp
> +< ts->sigaltstack_used.ss_size);
> }
>
> int sas_ss_flags(unsigned long sp)
> {
> -return (target_sigaltstack_used.ss_size == 0 ? SS_DISABLE
> +TaskState *ts = (TaskState *)thread_cpu->opaque;
> +
> +return (ts->sigaltstack_used.ss_size == 0 ? SS_DISABLE
>
