[PATCH v2 1/4] syscalls: Restore address limit after a syscall
From: Thomas Garnier <hidden>
Date: 2017-03-09 01:24:53
Subsystem:
abi/api, the rest · Maintainer:
Linus Torvalds
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 <redacted> --- 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