Adds a new return value to seccomp filters that triggers a SIGTRAP to be delivered with the new TRAP_SECCOMP si_code. This allows in-process system call emulation -- including just specifying an errno or cleanly dumping core -- rather than just dying. Supporting this change requires that secure_computing returns a value. This change adds an int return value and creates a new __secure_computing_int and deprecates the old __secure_computing call. This allows for piecemeal arch updating using HAVE_ARCH_SECCOMP_FILTER. (If -1 is returned, the system call must be skipped.) Note, the addition of TRAP_SECCOMP may not be appropriate. There are GNU specific extensions in place (e.g., TRAP_HWBKPT), but I'm not sure how sacred the definitions are. If it would be preferable to add a brand new si_code independent of the TRAP_* or use the unused si_errno (with ENOSYS), or do something totally different, please let me know! v8: - clean up based on changes to dependent patches v7: - introduction Signed-off-by: Will Drewry <wad@xxxxxxxxxxxx> --- arch/Kconfig | 8 ++++---- include/asm-generic/siginfo.h | 3 ++- include/linux/seccomp.h | 1 + kernel/seccomp.c | 20 ++++++++++++++++++++ 4 files changed, 27 insertions(+), 5 deletions(-) diff --git a/arch/Kconfig b/arch/Kconfig index 3f3052b..a01c151 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -203,10 +203,10 @@ config HAVE_ARCH_SECCOMP_FILTER bool help This symbol should be selected by an architecure if it provides - asm/syscall.h, specifically syscall_get_arguments() and - syscall_set_return_value(). Additionally, its system call - entry path must respect a return value of -1 from - __secure_computing_int() and/or secure_computing(). + asm/syscall.h, specifically syscall_get_arguments(), + syscall_set_return_value(), and syscall_rollback(). + Additionally, its system call entry path must respect a return + value of -1 from __secure_computing_int() and/or secure_computing(). config SECCOMP_FILTER def_bool y diff --git a/include/asm-generic/siginfo.h b/include/asm-generic/siginfo.h index 0dd4e87..a6c51a6 100644 --- a/include/asm-generic/siginfo.h +++ b/include/asm-generic/siginfo.h @@ -207,7 +207,8 @@ typedef struct siginfo { #define TRAP_TRACE (__SI_FAULT|2) /* process trace trap */ #define TRAP_BRANCH (__SI_FAULT|3) /* process taken branch trap */ #define TRAP_HWBKPT (__SI_FAULT|4) /* hardware breakpoint/watchpoint */ -#define NSIGTRAP 4 +#define TRAP_SECCOMP (__SI_FAULT|5) /* secure computing trap */ +#define NSIGTRAP 5 /* * SIGCHLD si_codes diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h index 879ece2..1be562f 100644 --- a/include/linux/seccomp.h +++ b/include/linux/seccomp.h @@ -19,6 +19,7 @@ * selects the least permissive choice. */ #define SECCOMP_RET_KILL 0x00000000U /* kill the task immediately */ +#define SECCOMP_RET_TRAP 0x00020000U /* disallow and send sigtrap */ #define SECCOMP_RET_ERRNO 0x00030000U /* returns an errno */ #define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */ diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 55d000d..c75485c 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -290,6 +290,21 @@ void copy_seccomp(struct seccomp *child, child->mode = prev->mode; child->filter = get_seccomp_filter(prev->filter); } + +/** + * seccomp_send_sigtrap - signals the task to allow in-process syscall emulation + * + * Forces a SIGTRAP with si_code of TRAP_SECCOMP. + */ +static void seccomp_send_sigtrap(void) +{ + struct siginfo info; + memset(&info, 0, sizeof(info)); + info.si_signo = SIGTRAP; + info.si_code = TRAP_SECCOMP; + info.si_addr = (void __user *)KSTK_EIP(current); + force_sig_info(SIGTRAP, &info, current); +} #endif /* CONFIG_SECCOMP_FILTER */ /* @@ -343,6 +358,11 @@ int __secure_computing_int(int this_syscall) -(action & SECCOMP_RET_DATA), 0); return -1; + case SECCOMP_RET_TRAP: + /* Show the handler the original registers. */ + syscall_rollback(current, task_pt_regs(current)); + seccomp_send_sigtrap(); + return -1; case SECCOMP_RET_ALLOW: return 0; case SECCOMP_RET_KILL: -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html