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Message-Id: <20170410164420.64003-1-thgarnie@google.com>
Date: Mon, 10 Apr 2017 09:44:17 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Arnd Bergmann <arnd@...db.de>,
Dave Hansen <dave.hansen@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Garnier <thgarnie@...gle.com>,
David Howells <dhowells@...hat.com>,
René Nyffenegger <mail@...enyffenegger.ch>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Oleg Nesterov <oleg@...hat.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Kees Cook <keescook@...omium.org>,
Rik van Riel <riel@...hat.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Brian Gerst <brgerst@...il.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Russell King <linux@...linux.org.uk>,
Will Deacon <will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>,
Mark Rutland <mark.rutland@....com>,
James Morse <james.morse@....com>
Cc: linux-s390@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-api@...r.kernel.org,
x86@...nel.org,
linux-arm-kernel@...ts.infradead.org,
kernel-hardening@...ts.openwall.com
Subject: [PATCH v7 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
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>
Tested-by: Kees Cook <keescook@...omium.org>
---
Based on next-20170410
---
arch/s390/Kconfig | 1 +
include/linux/syscalls.h | 26 +++++++++++++++++++++++++-
init/Kconfig | 6 ++++++
kernel/sys.c | 13 +++++++++++++
4 files changed, 45 insertions(+), 1 deletion(-)
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index d25435d94b6e..489a0cc6e46b 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -103,6 +103,7 @@ config S390
select ARCH_INLINE_WRITE_UNLOCK_BH
select ARCH_INLINE_WRITE_UNLOCK_IRQ
select ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE
+ select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
select ARCH_SAVE_PAGE_KEYS if HIBERNATION
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 980c3c9b06f8..801a7a74fe28 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -191,6 +191,27 @@ extern struct trace_event_functions exit_syscall_print_funcs;
SYSCALL_METADATA(sname, x, __VA_ARGS__) \
__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
+
+/*
+ * Called before coming back to user-mode. Returning to user-mode with an
+ * address limit different than USER_DS can allow to overwrite kernel memory.
+ */
+static inline void verify_pre_usermode_state(void) {
+ BUG_ON(!segment_eq(get_fs(), USER_DS));
+}
+
+#ifndef CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
+#define __CHECK_USER_CALLER() \
+ bool user_caller = segment_eq(get_fs(), USER_DS)
+#define __VERIFY_PRE_USERMODE_STATE() \
+ if (user_caller) verify_pre_usermode_state()
+#else
+#define __CHECK_USER_CALLER()
+#define __VERIFY_PRE_USERMODE_STATE()
+asmlinkage void address_limit_check_failed(void);
+#endif
+
+
#define __PROTECT(...) asmlinkage_protect(__VA_ARGS__)
#define __SYSCALL_DEFINEx(x, name, ...) \
asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
@@ -199,7 +220,10 @@ 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__)) \
{ \
- long ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
+ long ret; \
+ __CHECK_USER_CALLER(); \
+ ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
+ __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 7f7027817bce..e5fbd0becfa7 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1958,6 +1958,12 @@ config PROFILING
config TRACEPOINTS
bool
+config ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
+ bool
+ help
+ Disable the generic pre-usermode state verification. Allow each
+ architecture to optimize how and when the verification is done.
+
source "arch/Kconfig"
endmenu # General setup
diff --git a/kernel/sys.c b/kernel/sys.c
index 196c7134bee6..d30530ff8166 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2459,3 +2459,16 @@ COMPAT_SYSCALL_DEFINE1(sysinfo, struct compat_sysinfo __user *, info)
return 0;
}
#endif /* CONFIG_COMPAT */
+
+#ifdef CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
+/*
+ * This function is called when an architecture specific implementation detected
+ * an invalid address limit. The generic user-mode state checker will finish on
+ * the appropriate BUG_ON.
+ */
+asmlinkage void address_limit_check_failed(void)
+{
+ verify_pre_usermode_state();
+ panic("address_limit_check_failed called with a valid user-mode state");
+}
+#endif
--
2.12.2.715.g7642488e1d-goog
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