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Date: Thu, 12 Apr 2012 16:48:03 -0500
From: Will Drewry <wad@...omium.org>
To: linux-kernel@...r.kernel.org
Cc: linux-man@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-arch@...r.kernel.org,
	linux-doc@...r.kernel.org,
	kernel-hardening@...ts.openwall.com,
	netdev@...r.kernel.org,
	x86@...nel.org,
	arnd@...db.de,
	davem@...emloft.net,
	hpa@...or.com,
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	peterz@...radead.org,
	rdunlap@...otime.net,
	mcgrathr@...omium.org,
	tglx@...utronix.de,
	luto@....edu,
	eparis@...hat.com,
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	djm@...drot.org,
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	keescook@...omium.org,
	jmorris@...ei.org,
	Will Drewry <wad@...omium.org>
Subject: [PATCH v18 14/15] x86: Enable HAVE_ARCH_SECCOMP_FILTER

Enable support for seccomp filter on x86:
- syscall_get_arch()
- syscall_get_arguments()
- syscall_rollback()
- syscall_set_return_value()
- SIGSYS siginfo_t support
- secure_computing is called from a ptrace_event()-safe context
- secure_computing return value is checked (see below).

SECCOMP_RET_TRACE and SECCOMP_RET_TRAP may result in seccomp needing to
skip a system call without killing the process.  This is done by
returning a non-zero (-1) value from secure_computing.  This change
makes x86 respect that return value.

To ensure that minimal kernel code is exposed, a non-zero return value
results in an immediate return to user space (with an invalid syscall
number).

Signed-off-by: Will Drewry <wad@...omium.org>
Reviewed-by: H. Peter Anvin <hpa@...or.com>
Acked-by: Eric Paris <eparis@...hat.com>

v18: rebase and tweaked change description, acked-by
v17: added reviewed by and rebased
v..: all rebases since original introduction.
---
 arch/x86/Kconfig         |    1 +
 arch/x86/kernel/ptrace.c |    7 ++++++-
 2 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1d14cc6..3a41c44 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -82,6 +82,7 @@ config X86
 	select ARCH_HAVE_NMI_SAFE_CMPXCHG
 	select GENERIC_IOMAP
 	select DCACHE_WORD_ACCESS if !DEBUG_PAGEALLOC
+	select HAVE_ARCH_SECCOMP_FILTER
 
 config INSTRUCTION_DECODER
 	def_bool (KPROBES || PERF_EVENTS)
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 685845c..13b1990 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1480,7 +1480,11 @@ long syscall_trace_enter(struct pt_regs *regs)
 		regs->flags |= X86_EFLAGS_TF;
 
 	/* do the secure computing check first */
-	secure_computing(regs->orig_ax);
+	if (secure_computing(regs->orig_ax)) {
+		/* seccomp failures shouldn't expose any additional code. */
+		ret = -1L;
+		goto out;
+	}
 
 	if (unlikely(test_thread_flag(TIF_SYSCALL_EMU)))
 		ret = -1L;
@@ -1505,6 +1509,7 @@ long syscall_trace_enter(struct pt_regs *regs)
 				    regs->dx, regs->r10);
 #endif
 
+out:
 	return ret ?: regs->orig_ax;
 }
 
-- 
1.7.5.4

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