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Message-Id: <20170309012456.5631-1-thgarnie@google.com>
Date: Wed, 8 Mar 2017 17:24:53 -0800
From: Thomas Garnier <thgarnie@...gle.com>
To: David Howells <dhowells@...hat.com>,
Dave Hansen <dave.hansen@...el.com>,
Arnd Bergmann <arnd@...db.de>,
Al Viro <viro@...iv.linux.org.uk>,
René Nyffenegger <mail@...enyffenegger.ch>,
Thomas Garnier <thgarnie@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Kees Cook <keescook@...omium.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
"David S . Miller" <davem@...emloft.net>,
Andy Lutomirski <luto@...nel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Nicolas Pitre <nicolas.pitre@...aro.org>,
Petr Mladek <pmladek@...e.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Helge Deller <deller@....de>,
Rik van Riel <riel@...hat.com>,
Ingo Molnar <mingo@...nel.org>,
Oleg Nesterov <oleg@...hat.com>,
John Stultz <john.stultz@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
Paolo Bonzini <pbonzini@...hat.com>,
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"Luis R . Rodriguez" <mcgrof@...nel.org>,
He Chen <he.chen@...ux.intel.com>,
Russell King <linux@...linux.org.uk>,
Will Deacon <will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>,
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Pratyush Anand <panand@...hat.com>,
Vladimir Murzin <vladimir.murzin@....com>,
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Andre Przywara <andre.przywara@....com>
Cc: linux-api@...r.kernel.org,
linux-kernel@...r.kernel.org,
x86@...nel.org,
linux-arm-kernel@...ts.infradead.org,
kernel-hardening@...ts.openwall.com
Subject: [PATCH v2 1/4] syscalls: Restore address limit after a syscall
This patch ensures a syscall does not return to user-mode with a kernel
address limit. If that happened, a process can corrupt kernel-mode
memory and elevate privileges.
For example, it would mitigation this bug:
- https://bugs.chromium.org/p/project-zero/issues/detail?id=990
If the CONFIG_BUG_ON_DATA_CORRUPTION option is enabled, an incorrect
state will result in a BUG_ON.
The CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE option is also
added so each architecture can optimize this change.
Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
Based on next-20170308
---
include/linux/syscalls.h | 19 +++++++++++++++++++
init/Kconfig | 7 +++++++
kernel/sys.c | 8 ++++++++
3 files changed, 34 insertions(+)
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 980c3c9b06f8..78a2268ecd6e 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -191,6 +191,22 @@ extern struct trace_event_functions exit_syscall_print_funcs;
SYSCALL_METADATA(sname, x, __VA_ARGS__) \
__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
+asmlinkage void verify_pre_usermode_state(void);
+
+#ifndef CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
+static inline bool has_user_ds(void) {
+ bool ret = segment_eq(get_fs(), USER_DS);
+ // Prevent re-ordering the call
+ barrier();
+ return ret;
+}
+#else
+static inline bool has_user_ds(void) {
+ return false;
+}
+#endif
+
+
#define __PROTECT(...) asmlinkage_protect(__VA_ARGS__)
#define __SYSCALL_DEFINEx(x, name, ...) \
asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
@@ -199,7 +215,10 @@ extern struct trace_event_functions exit_syscall_print_funcs;
asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
{ \
+ bool user_caller = has_user_ds(); \
long ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
+ if (user_caller) \
+ verify_pre_usermode_state(); \
__MAP(x,__SC_TEST,__VA_ARGS__); \
__PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \
return ret; \
diff --git a/init/Kconfig b/init/Kconfig
index c859c993c26f..c4efc3a95e4a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1929,6 +1929,13 @@ config PROFILING
config TRACEPOINTS
bool
+#
+# Set by each architecture that want to optimize how verify_pre_usermode_state
+# is called.
+#
+config ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
+ bool
+
source "arch/Kconfig"
endmenu # General setup
diff --git a/kernel/sys.c b/kernel/sys.c
index 196c7134bee6..411163ac9dc3 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2459,3 +2459,11 @@ COMPAT_SYSCALL_DEFINE1(sysinfo, struct compat_sysinfo __user *, info)
return 0;
}
#endif /* CONFIG_COMPAT */
+
+/* Called before coming back to user-mode */
+asmlinkage void verify_pre_usermode_state(void)
+{
+ if (CHECK_DATA_CORRUPTION(!segment_eq(get_fs(), USER_DS),
+ "incorrect get_fs() on user-mode return"))
+ set_fs(USER_DS);
+}
--
2.12.0.246.ga2ecc84866-goog
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