| Message ID | 20201127193238.821364-5-krisman@collabora.com |
|---|---|
| State | New |
| Headers | show |
| Series | None | expand |
On Fri, Nov 27, 2020 at 02:32:35PM -0500, Gabriel Krisman Bertazi wrote: > Syscall User Dispatch (SUD) must take precedence over seccomp and > ptrace, since the use case is emulation (it can be invoked with a > different ABI) such that seccomp filtering by syscall number doesn't > make sense in the first place. In addition, either the syscall is > dispatched back to userspace, in which case there is no resource for to > trace, or the syscall will be executed, and seccomp/ptrace will execute > next. > > Since SUD runs before tracepoints, it needs to be a SYSCALL_WORK_EXIT as > well, just to prevent a trace exit event when dispatch was triggered. > For that, the on_syscall_dispatch() examines context to skip the > tracepoint, audit and other work. > > Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com> Acked-by: Kees Cook <keescook@chromium.org> -- Kees Cook
On Fri, Nov 27, 2020 at 11:33 AM Gabriel Krisman Bertazi <krisman@collabora.com> wrote: > > Syscall User Dispatch (SUD) must take precedence over seccomp and > ptrace, since the use case is emulation (it can be invoked with a > different ABI) such that seccomp filtering by syscall number doesn't > make sense in the first place. In addition, either the syscall is > dispatched back to userspace, in which case there is no resource for to > trace, or the syscall will be executed, and seccomp/ptrace will execute > next. > > Since SUD runs before tracepoints, it needs to be a SYSCALL_WORK_EXIT as > well, just to prevent a trace exit event when dispatch was triggered. > For that, the on_syscall_dispatch() examines context to skip the > tracepoint, audit and other work. > > Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com> > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > Changes since v6: > - Update do_syscall_intercept signature (Christian Brauner) > - Move it to before tracepoints > - Use SYSCALL_WORK flags > --- > include/linux/entry-common.h | 2 ++ > kernel/entry/common.c | 17 +++++++++++++++++ > 2 files changed, 19 insertions(+) > > diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h > index 49b26b216e4e..a6e98b4ba8e9 100644 > --- a/include/linux/entry-common.h > +++ b/include/linux/entry-common.h > @@ -44,10 +44,12 @@ > SYSCALL_WORK_SYSCALL_TRACE | \ > SYSCALL_WORK_SYSCALL_EMU | \ > SYSCALL_WORK_SYSCALL_AUDIT | \ > + SYSCALL_WORK_SYSCALL_USER_DISPATCH | \ > ARCH_SYSCALL_WORK_ENTER) > #define SYSCALL_WORK_EXIT (SYSCALL_WORK_SYSCALL_TRACEPOINT | \ > SYSCALL_WORK_SYSCALL_TRACE | \ > SYSCALL_WORK_SYSCALL_AUDIT | \ > + SYSCALL_WORK_SYSCALL_USER_DISPATCH | \ > ARCH_SYSCALL_WORK_EXIT) > > /* > diff --git a/kernel/entry/common.c b/kernel/entry/common.c > index f1b12dc32ff4..ec20aba3b890 100644 > --- a/kernel/entry/common.c > +++ b/kernel/entry/common.c > @@ -6,6 +6,8 @@ > #include <linux/livepatch.h> > #include <linux/audit.h> > > +#include "common.h" > + > #define CREATE_TRACE_POINTS > #include <trace/events/syscalls.h> > > @@ -47,6 +49,16 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall, > { > long ret = 0; > > + /* > + * Handle Syscall User Dispatch. This must comes first, since > + * the ABI here can be something that doesn't make sense for > + * other syscall_work features. > + */ > + if (work & SYSCALL_WORK_SYSCALL_USER_DISPATCH) { > + if (do_syscall_user_dispatch(regs)) > + return -1L; > + } > + > /* Handle ptrace */ > if (work & (SYSCALL_WORK_SYSCALL_TRACE | SYSCALL_WORK_SYSCALL_EMU)) { > ret = arch_syscall_enter_tracehook(regs); > @@ -232,6 +244,11 @@ static void syscall_exit_work(struct pt_regs *regs, unsigned long work) > { > bool step; > > + if (work & SYSCALL_WORK_SYSCALL_USER_DISPATCH) { > + if (on_syscall_dispatch()) > + return; > + } I think this would be less confusing if you just open-coded the body of on_syscall_dispatch here and got rid of the helper. --Andy
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h index 49b26b216e4e..a6e98b4ba8e9 100644 --- a/include/linux/entry-common.h +++ b/include/linux/entry-common.h @@ -44,10 +44,12 @@ SYSCALL_WORK_SYSCALL_TRACE | \ SYSCALL_WORK_SYSCALL_EMU | \ SYSCALL_WORK_SYSCALL_AUDIT | \ + SYSCALL_WORK_SYSCALL_USER_DISPATCH | \ ARCH_SYSCALL_WORK_ENTER) #define SYSCALL_WORK_EXIT (SYSCALL_WORK_SYSCALL_TRACEPOINT | \ SYSCALL_WORK_SYSCALL_TRACE | \ SYSCALL_WORK_SYSCALL_AUDIT | \ + SYSCALL_WORK_SYSCALL_USER_DISPATCH | \ ARCH_SYSCALL_WORK_EXIT) /* diff --git a/kernel/entry/common.c b/kernel/entry/common.c index f1b12dc32ff4..ec20aba3b890 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -6,6 +6,8 @@ #include <linux/livepatch.h> #include <linux/audit.h> +#include "common.h" + #define CREATE_TRACE_POINTS #include <trace/events/syscalls.h> @@ -47,6 +49,16 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall, { long ret = 0; + /* + * Handle Syscall User Dispatch. This must comes first, since + * the ABI here can be something that doesn't make sense for + * other syscall_work features. + */ + if (work & SYSCALL_WORK_SYSCALL_USER_DISPATCH) { + if (do_syscall_user_dispatch(regs)) + return -1L; + } + /* Handle ptrace */ if (work & (SYSCALL_WORK_SYSCALL_TRACE | SYSCALL_WORK_SYSCALL_EMU)) { ret = arch_syscall_enter_tracehook(regs); @@ -232,6 +244,11 @@ static void syscall_exit_work(struct pt_regs *regs, unsigned long work) { bool step; + if (work & SYSCALL_WORK_SYSCALL_USER_DISPATCH) { + if (on_syscall_dispatch()) + return; + } + audit_syscall_exit(regs); if (work & SYSCALL_WORK_SYSCALL_TRACEPOINT)