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Port seccomp acceleration to Linux 3.5.0
* etc/NEWS: Update correspondingly. * exec/Makefile.in (config-mips.m4): Don't define rule or predicate $(LOADOBJS) on it elsewhere than on MIPS. * exec/README: Direct developers to GDB. * exec/trace.c (finish_exec): Resume the tracee after reporting an error in `exec'. (after_fork): If seccomp is enabled on Android, and the kernel is 4.7 or earlier, detect whether revisions to the sequencing of seccomp events have been backported from 4.8. (exec_waitpid): Resume the process with PTRACE_CONT after receiving an unknown signal. (exec_init): Cease disabling seccomp on Android kernels earlier than 4.8.
This commit is contained in:
Po Lu
parent
e087d3009b
commit
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2
etc/NEWS
2
etc/NEWS
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@ -59,7 +59,7 @@ default), the 'whitespace-cleanup' function will now add the newline.
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** Process execution has been optimized on Android.
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The run-time performance of subprocesses on recent Android releases
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where a userspace executable loader is required has been optimized on
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systems featuring Linux 4.8.0 and above.
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systems featuring Linux 3.5.0 and above.
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----------------------------------------------------------------------
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@ -90,16 +90,16 @@ ifeq ($(is_mips),yes)
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.s.o:
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$(M4) $< > $(notdir $<).s
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$(AS) $(ASFLAGS) $(notdir $<).s -o $@
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else
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.s.o:
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$(AS) $(ASFLAGS) $< -o $@
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endif
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# Set up dependencies for config-mips.m4.
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config-mips.m4: config-mips.m4.in
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cd $(srcdir) && ./config.status $@
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$(LOADOBJS): config-mips.m4
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else
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.s.o:
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$(AS) $(ASFLAGS) $< -o $@
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endif
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# Set up rules to build libexec.a.
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@ -1,3 +1,6 @@
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This directory holds the source code to a library used to replace the
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`execve' and `execveat' system calls, used by the Android port of
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Emacs to start executables without intervention from the system.
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The most edifying resource for developers will be GDB, or to be precise,
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the Linux target implementations for architectures of interest.
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113
exec/trace.c
113
exec/trace.c
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@ -845,7 +845,12 @@ finish_exec (struct exec_tracee *tracee, USER_REGS_STRUCT *regs)
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#else /* !__aarch64__ */
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ptrace (PTRACE_SETREGS, tracee->pid, NULL, regs);
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#endif /* __aarch64__ */
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return;
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/* Continue; not much in the way of remediation is available if
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either of PTRACE_SETREGS and this resumption fails. */
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ptrace ((use_seccomp_p ? PTRACE_CONT : PTRACE_SYSCALL),
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tracee->pid, 0, 0);
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goto error;
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}
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/* Write the loader area to the stack, followed by its size and the
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@ -1858,6 +1863,10 @@ after_fork (pid_t pid)
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{
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int wstatus, rc, flags;
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struct exec_tracee *tracee;
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#if defined HAVE_SECCOMP && __ANDROID__
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int statusarg;
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USER_REGS_STRUCT regs;
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#endif /* defined HAVE_SECCOMP && __ANDROID__ */
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/* First, wait for something to happen to PID. */
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again:
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@ -1897,14 +1906,86 @@ after_fork (pid_t pid)
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return 1;
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}
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/* Request that the child stop upon the next system call, or the next
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filter event. */
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rc = ptrace ((use_seccomp_p ? PTRACE_CONT : PTRACE_SYSCALL),
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pid, 0, 0);
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#if defined HAVE_SECCOMP && __ANDROID__
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/* Certain Android kernels have received backports of those new
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PTRACE_EVENT_SECCOMP semantics which were introduced in kernel
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version 4.8, so that it is necessary to actively establish which
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variant is in place. */
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if (kernel_4_7_or_earlier && use_seccomp_p)
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{
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/* Request that the child stop upon the next `exec' system call,
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one of which is assumed to always be issued by the child, as
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below, but await the next stop, and examine its contents.
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Anciently, the syscall-stop preceeded events marked
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PTRACE_EVENT_SECCOMP, whereas this sequence is reversed in
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4.8+, and in releases with these changes backported. */
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rc = ptrace (PTRACE_SYSCALL, pid, 0, 0);
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if (rc)
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return 1;
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while (true)
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{
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rc = waitpid (pid, &wstatus, __WALL);
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if (rc != pid)
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return 1;
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if (WIFSTOPPED (wstatus))
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{
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/* Verify that this system call is `exec', not one issued
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between PTRACE_TRACEME and `exec' intercepted by
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PTRACE_SYSCALL. */
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#ifdef __aarch64__
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rc = aarch64_get_regs (pid, ®s);
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#else /* !__aarch64__ */
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rc = ptrace (PTRACE_GETREGS, pid, NULL, ®s);
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#endif /* __aarch64__ */
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if (rc)
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return 1;
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if (regs.SYSCALL_NUM_REG == EXEC_SYSCALL)
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{
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statusarg = ((wstatus & 0xfff00) >> 8);
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if (statusarg == (SIGTRAP | (PTRACE_EVENT_SECCOMP << 8)))
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{
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/* The first event to be delivered is a seccomp
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stop, indicating that this is an unmodified
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<4.7 kernel. Return to await the subsequent
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syscall-stop, which should be received and
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acted on by process_system_call. */
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rc = ptrace (PTRACE_SYSCALL, pid, 0, 0);
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break;
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}
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else if (statusarg == (SIGTRAP | 0x80))
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{
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/* Syscall-traps take priority. This is a
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doctored 4.7 kernel. */
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kernel_4_7_or_earlier = false;
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rc = ptrace (PTRACE_CONT, pid, 0, 0);
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break;
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}
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}
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rc = ptrace (PTRACE_SYSCALL, pid, 0, 0);
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if (rc)
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return 1;
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}
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else
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return 1;
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}
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}
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else
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#endif /* HAVE_SECCOMP && __ANDROID__ */
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/* Request that the child stop upon the next system call, or the
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next filter event. */
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rc = ptrace ((use_seccomp_p ? PTRACE_CONT : PTRACE_SYSCALL),
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pid, 0, 0);
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if (rc)
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return 1;
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/* Enter the child in `tracing_processes'. */
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/* Enroll the child into `tracing_processes'. */
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if (free_tracees)
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{
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@ -2064,8 +2145,9 @@ exec_waitpid (pid_t pid, int *wstatus, int options)
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#endif /* SIGSYS */
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default:
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/* Continue the process until the next syscall. */
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ptrace (PTRACE_SYSCALL, pid, 0, status);
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/* Resume the process as appropriate. */
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ptrace ((use_seccomp_p ? PTRACE_CONT : PTRACE_SYSCALL),
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pid, 0, status);
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return -1;
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}
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}
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@ -2117,20 +2199,7 @@ exec_init (const char *loader)
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else
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{
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if (major < 4 || (major == 4 && minor <= 7))
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{
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#ifndef __ANDROID__
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kernel_4_7_or_earlier = true;
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#else /* __ANDROID __ */
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/* Certain Android kernels have received backports of
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those new PTRACE_EVENT_SECCOMP semantics which were
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introduced in kernel version 4.8, so that it is
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necessary to actively establish which variant is in
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place. This being much too involved for code I cannot
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test, simply disable seccomp on kernel releases subject
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to these uncertainties. */
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use_seccomp_p = false;
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#endif /* !__ANDROID__ */
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}
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kernel_4_7_or_earlier = true;
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}
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}
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#endif /* HAVE_SECCOMP */
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