Re: [PATCH] Kernel: Audit Support For The ARM Platform (Re-post requested)

This patch provides functionality to audit system call events on the ARM platform. The implementation was based off the structure of the MIPS platform and information in this (http://lists.fedoraproject.org/pipermail/arm/2009-October/000382.html) mailing list thread. The required audit_syscall_exit and audit_syscall_entry checks were added to ptrace using the standard registers for system call values (r0 through r3). A thread information flag was added for auditing (TIF_SYSCALL_AUDIT) and a meta-flag was added (_TIF_SYSCALL_WORK) to simplify modifications to the syscall entry/exit. Now, if either the TRACE flag is set or the AUDIT flag is set, the syscall_trace function will be executed. The prober changes were made to Kconfig to allow CONFIG_AUDITSYSCALL to be enabled. Due to platform availability limitations, this patch was only tested on the Android platform running the modified "android-goldfish-2.6.29" kernel. A test compile was performed using Code Sourcery's cross-compilation toolset and the current linux-3.0 stable kernel. The changes compile without error. I'm hoping, due to the simple modifications, the patch is "obviously correct". Signed-off-by: Nathaniel Husted <nhusted(a)gmail.com&gt; --- diff -uprN -X linux-3.0-vanilla/Documentation/dontdiff linux-3.0-vanilla/arch/arm/include/asm/thread_info.h linux-3.0-modified/arch/arm/include/asm/thread_info.h --- linux-3.0-vanilla/arch/arm/include/asm/thread_info.h 2011-07-21 19:17:23.000000000 -0700 +++ linux-3.0-modified/arch/arm/include/asm/thread_info.h 2011-08-02 14:04:29.005599252 -0700 @@ -129,6 +129,7 @@ extern void vfp_flush_hwstate(struct thr /* * thread information flags: * TIF_SYSCALL_TRACE - syscall trace active + * TIF_SYSCAL_AUDIT - syscall auditing active * TIF_SIGPENDING - signal pending * TIF_NEED_RESCHED - rescheduling necessary * TIF_NOTIFY_RESUME - callback before returning to user @@ -139,6 +140,7 @@ extern void vfp_flush_hwstate(struct thr #define TIF_NEED_RESCHED 1 #define TIF_NOTIFY_RESUME 2 /* callback before returning to user */ #define TIF_SYSCALL_TRACE 8 +#define TIF_SYSCALL_AUDIT 9 #define TIF_POLLING_NRFLAG 16 #define TIF_USING_IWMMXT 17 #define TIF_MEMDIE 18 /* is terminating due to OOM killer */ @@ -150,12 +152,17 @@ extern void vfp_flush_hwstate(struct thr #define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED) #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME) #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE) +#define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT) + #define _TIF_POLLING_NRFLAG (1 << TIF_POLLING_NRFLAG) #define _TIF_USING_IWMMXT (1 << TIF_USING_IWMMXT) #define _TIF_FREEZE (1 << TIF_FREEZE) #define _TIF_RESTORE_SIGMASK (1 << TIF_RESTORE_SIGMASK) #define _TIF_SECCOMP (1 << TIF_SECCOMP) +/* Checks for any syscall work in entry-common.S */ +#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT) + /* * Change these and you break ASM code in entry-common.S */ diff -uprN -X linux-3.0-vanilla/Documentation/dontdiff linux-3.0-vanilla/arch/arm/kernel/entry-common.S linux-3.0-modified/arch/arm/kernel/entry-common.S --- linux-3.0-vanilla/arch/arm/kernel/entry-common.S 2011-07-21 19:17:23.000000000 -0700 +++ linux-3.0-modified/arch/arm/kernel/entry-common.S 2011-08-02 14:01:28.747720225 -0700 @@ -87,7 +87,7 @@ ENTRY(ret_from_fork) get_thread_info tsk ldr r1, [tsk, #TI_FLAGS] @ check for syscall tracing mov why, #1 - tst r1, #_TIF_SYSCALL_TRACE @ are we tracing syscalls? + tst r1, #_TIF_SYSCALL_WORK @ are we tracing syscalls? beq ret_slow_syscall mov r1, sp mov r0, #1 @ trace exit [IP = 1] @@ -443,7 +443,7 @@ ENTRY(vector_swi) 1: #endif - tst r10, #_TIF_SYSCALL_TRACE @ are we tracing syscalls? + tst r10, #_TIF_SYSCALL_WORK @ are we tracing syscalls? bne __sys_trace cmp scno, #NR_syscalls @ check upper syscall limit diff -uprN -X linux-3.0-vanilla/Documentation/dontdiff linux-3.0-vanilla/arch/arm/kernel/ptrace.c linux-3.0-modified/arch/arm/kernel/ptrace.c --- linux-3.0-vanilla/arch/arm/kernel/ptrace.c 2011-07-21 19:17:23.000000000 -0700 +++ linux-3.0-modified/arch/arm/kernel/ptrace.c 2011-08-02 14:44:09.949722828 -0700 @@ -926,11 +926,6 @@ asmlinkage int syscall_trace(int why, st { unsigned long ip; - if (!test_thread_flag(TIF_SYSCALL_TRACE)) - return scno; - if (!(current->ptrace & PT_PTRACED)) - return scno; - /* * Save IP. IP is used to denote syscall entry/exit: * IP = 0 -> entry, = 1 -> exit @@ -938,6 +933,25 @@ asmlinkage int syscall_trace(int why, st ip = regs->ARM_ip; regs->ARM_ip = why; + /* perform a secure computing check first */ + if (regs->ARM_ip) + secure_computing(scno);

+ + if (unlikely(current->audit_context)) { + if (!ip) + audit_syscall_exit(AUDITSC_RESULT(regs->ARM_r0), + regs->ARM_r0); + else + audit_syscall_entry(AUDIT_ARCH_ARMEB, scno, + regs->ARM_r0, regs->ARM_r1, + regs->ARM_r2, regs->ARM_r3); + } + + if (!test_thread_flag(TIF_SYSCALL_TRACE)) + return scno; + if (!(current->ptrace & PT_PTRACED)) + return scno; + current_thread_info()->syscall = scno; /* the 0x80 provides a way for the tracing parent to distinguish diff -uprN -X linux-3.0-vanilla/Documentation/dontdiff linux-3.0-vanilla/init/Kconfig linux-3.0-modified/init/Kconfig --- linux-3.0-vanilla/init/Kconfig 2011-07-21 19:17:23.000000000 -0700 +++ linux-3.0-modified/init/Kconfig 2011-08-02 14:02:06.359364526 -0700 @@ -355,7 +355,7 @@ config AUDIT config AUDITSYSCALL bool "Enable system-call auditing support" - depends on AUDIT && (X86 || PPC || S390 || IA64 || UML || SPARC64 || SUPERH) + depends on AUDIT && (X86 || PPC || S390 || IA64 || UML || SPARC64 || SUPERH || ARM) default y if SECURITY_SELINUX help Enable low-overhead system-call auditing infrastructure that