| Message ID | 1404459115-8292-3-git-send-email-takahiro.akashi@linaro.org |
|---|---|
| State | New |
| Headers | show |
Hi Akashi, On Fri, Jul 04, 2014 at 08:31:55AM +0100, AKASHI Takahiro wrote: > secure_computing() should always be called first in syscall_trace_enter(). > If it returns non-zero, we should stop further handling. Then that system > call may eventually fail, be trapped or the process itself be killed > depending on loaded rules. > In this case, syscall_trace_enter() returns a dedicated value in order to > skip a normal syscall table lookup because a seccomp rule may have already > overridden errno. [...] > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c > index 70526cf..baab5fc 100644 > --- a/arch/arm64/kernel/ptrace.c > +++ b/arch/arm64/kernel/ptrace.c > @@ -21,12 +21,14 @@ > > #include <linux/audit.h> > #include <linux/compat.h> > +#include <linux/errno.h> > #include <linux/kernel.h> > #include <linux/sched.h> > #include <linux/mm.h> > #include <linux/smp.h> > #include <linux/ptrace.h> > #include <linux/user.h> > +#include <linux/seccomp.h> > #include <linux/security.h> > #include <linux/init.h> > #include <linux/signal.h> > @@ -1109,6 +1111,10 @@ static void tracehook_report_syscall(struct pt_regs *regs, > > asmlinkage int syscall_trace_enter(struct pt_regs *regs) > { > + if (secure_computing(regs->syscallno) == -1) > + /* seccomp failures shouldn't expose any additional code. */ > + return -EPERM; > + > if (test_thread_flag(TIF_SYSCALL_TRACE)) > tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER); We return regs->syscallno immediately after this, so we have the same issue that Kees identified for arch/arm/. Did you follow the discussion I had with Andy? Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Will, > (1) Updating syscallno based on w8, but this ties us to the current ABI > and could get messy if this register changes in the future. So, is this the conclusion that I should follow? -Takahiro AKASHI On 07/09/2014 01:12 PM, Will Deacon wrote: > Hi Akashi, > > On Fri, Jul 04, 2014 at 08:31:55AM +0100, AKASHI Takahiro wrote: >> secure_computing() should always be called first in syscall_trace_enter(). >> If it returns non-zero, we should stop further handling. Then that system >> call may eventually fail, be trapped or the process itself be killed >> depending on loaded rules. >> In this case, syscall_trace_enter() returns a dedicated value in order to >> skip a normal syscall table lookup because a seccomp rule may have already >> overridden errno. > > [...] > >> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c >> index 70526cf..baab5fc 100644 >> --- a/arch/arm64/kernel/ptrace.c >> +++ b/arch/arm64/kernel/ptrace.c >> @@ -21,12 +21,14 @@ >> >> #include <linux/audit.h> >> #include <linux/compat.h> >> +#include <linux/errno.h> >> #include <linux/kernel.h> >> #include <linux/sched.h> >> #include <linux/mm.h> >> #include <linux/smp.h> >> #include <linux/ptrace.h> >> #include <linux/user.h> >> +#include <linux/seccomp.h> >> #include <linux/security.h> >> #include <linux/init.h> >> #include <linux/signal.h> >> @@ -1109,6 +1111,10 @@ static void tracehook_report_syscall(struct pt_regs *regs, >> >> asmlinkage int syscall_trace_enter(struct pt_regs *regs) >> { >> + if (secure_computing(regs->syscallno) == -1) >> + /* seccomp failures shouldn't expose any additional code. */ >> + return -EPERM; >> + >> if (test_thread_flag(TIF_SYSCALL_TRACE)) >> tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER); > > We return regs->syscallno immediately after this, so we have the same issue > that Kees identified for arch/arm/. Did you follow the discussion I had with > Andy? > > Will > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
On Thu, Jul 10, 2014 at 05:33:50AM +0100, AKASHI Takahiro wrote: > Will, > > > (1) Updating syscallno based on w8, but this ties us to the current ABI > > and could get messy if this register changes in the future. > > So, is this the conclusion that I should follow? I think so, with the exception that if the tracer/debugger sets it to -1 to abort the syscall, then we should restore the original value. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 3a18571..eeac003 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -32,6 +32,7 @@ config ARM64 select HAVE_ARCH_AUDITSYSCALL select HAVE_ARCH_JUMP_LABEL select HAVE_ARCH_KGDB + select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_TRACEHOOK select HAVE_C_RECORDMCOUNT select HAVE_DEBUG_BUGVERBOSE @@ -259,6 +260,19 @@ config ARCH_HAS_CACHE_LINE_SIZE source "mm/Kconfig" +config SECCOMP + bool "Enable seccomp to safely compute untrusted bytecode" + ---help--- + This kernel feature is useful for number crunching applications + that may need to compute untrusted bytecode during their + execution. By using pipes or other transports made available to + the process as file descriptors supporting the read/write + syscalls, it's possible to isolate those applications in + their own address space using seccomp. Once seccomp is + enabled via prctl(PR_SET_SECCOMP), it cannot be disabled + and the task is only allowed to execute a few safe syscalls + defined by each seccomp mode. + config XEN_DOM0 def_bool y depends on XEN diff --git a/arch/arm64/include/asm/seccomp.h b/arch/arm64/include/asm/seccomp.h new file mode 100644 index 0000000..c76fac9 --- /dev/null +++ b/arch/arm64/include/asm/seccomp.h @@ -0,0 +1,25 @@ +/* + * arch/arm64/include/asm/seccomp.h + * + * Copyright (C) 2014 Linaro Limited + * Author: AKASHI Takahiro <takahiro.akashi@linaro.org> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ +#ifndef _ASM_SECCOMP_H +#define _ASM_SECCOMP_H + +#include <asm/unistd.h> + +#ifdef CONFIG_COMPAT +#define __NR_seccomp_read_32 __NR_compat_read +#define __NR_seccomp_write_32 __NR_compat_write +#define __NR_seccomp_exit_32 __NR_compat_exit +#define __NR_seccomp_sigreturn_32 __NR_compat_rt_sigreturn +#endif /* CONFIG_COMPAT */ + +#include <asm-generic/seccomp.h> + +#endif /* _ASM_SECCOMP_H */ diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h index c980ab7..729c155 100644 --- a/arch/arm64/include/asm/unistd.h +++ b/arch/arm64/include/asm/unistd.h @@ -31,6 +31,9 @@ * Compat syscall numbers used by the AArch64 kernel. */ #define __NR_compat_restart_syscall 0 +#define __NR_compat_exit 1 +#define __NR_compat_read 3 +#define __NR_compat_write 4 #define __NR_compat_sigreturn 119 #define __NR_compat_rt_sigreturn 173 diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 5141e79..fe55b4c 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -628,6 +628,10 @@ ENDPROC(el0_svc) __sys_trace: mov x0, sp bl syscall_trace_enter +#ifdef CONFIG_SECCOMP + cmp w0, #-EPERM // check seccomp result + b.eq ret_to_user // -EPERM means 'rejected' +#endif adr lr, __sys_trace_return // return address uxtw scno, w0 // syscall number (possibly new) mov x1, sp // pointer to regs diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 70526cf..baab5fc 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -21,12 +21,14 @@ #include <linux/audit.h> #include <linux/compat.h> +#include <linux/errno.h> #include <linux/kernel.h> #include <linux/sched.h> #include <linux/mm.h> #include <linux/smp.h> #include <linux/ptrace.h> #include <linux/user.h> +#include <linux/seccomp.h> #include <linux/security.h> #include <linux/init.h> #include <linux/signal.h> @@ -1109,6 +1111,10 @@ static void tracehook_report_syscall(struct pt_regs *regs, asmlinkage int syscall_trace_enter(struct pt_regs *regs) { + if (secure_computing(regs->syscallno) == -1) + /* seccomp failures shouldn't expose any additional code. */ + return -EPERM; + if (test_thread_flag(TIF_SYSCALL_TRACE)) tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
secure_computing() should always be called first in syscall_trace_enter(). If it returns non-zero, we should stop further handling. Then that system call may eventually fail, be trapped or the process itself be killed depending on loaded rules. In this case, syscall_trace_enter() returns a dedicated value in order to skip a normal syscall table lookup because a seccomp rule may have already overridden errno. Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> --- arch/arm64/Kconfig | 14 ++++++++++++++ arch/arm64/include/asm/seccomp.h | 25 +++++++++++++++++++++++++ arch/arm64/include/asm/unistd.h | 3 +++ arch/arm64/kernel/entry.S | 4 ++++ arch/arm64/kernel/ptrace.c | 6 ++++++ 5 files changed, 52 insertions(+) create mode 100644 arch/arm64/include/asm/seccomp.h