From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Garnier Subject: Re: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode Date: Fri, 5 May 2017 15:18:30 -0700 Message-ID: References: <20170428153213.137279-1-thgarnie@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: <20170428153213.137279-1-thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Martin Schwidefsky , Heiko Carstens , Dave Hansen , Arnd Bergmann , Thomas Gleixner , David Howells , Thomas Garnier , =?UTF-8?Q?Ren=C3=A9_Nyffenegger?= , Andrew Morton , "Paul E . McKenney" , Ingo Molnar , "Eric W . Biederman" , Oleg Nesterov , Pavel Tikhomirov , Ingo Molnar , "H . Peter Anvin" , Andy Lutomirski , Paolo Bonzini , Rik van Riel Cc: linux-s390 , LKML , Linux API , the arch/x86 maintainers , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Kernel Hardening List-Id: linux-api@vger.kernel.org On Fri, Apr 28, 2017 at 8:32 AM, Thomas Garnier wrote: > Ensure that a syscall does not return to user-mode with a kernel address > limit. If that happens, a process can corrupt kernel-mode memory and > elevate privileges [1]. > > The CONFIG_ADDR_LIMIT_CHECK option disables the generic check so each > architecture can create optimized versions. This option is enabled by > default on s390 because a similar feature already exists. > > [1] https://bugs.chromium.org/p/project-zero/issues/detail?id=990 > > Signed-off-by: Thomas Garnier > Tested-by: Kees Cook Ingo: Do you want to take the set? > --- > Based on next-20170426 > --- > arch/s390/Kconfig | 1 + > include/linux/syscalls.h | 27 ++++++++++++++++++++++++++- > init/Kconfig | 6 ++++++ > kernel/sys.c | 13 +++++++++++++ > 4 files changed, 46 insertions(+), 1 deletion(-) > > diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig > index d25435d94b6e..3d2ec084d5fc 100644 > --- a/arch/s390/Kconfig > +++ b/arch/s390/Kconfig > @@ -64,6 +64,7 @@ config ARCH_SUPPORTS_UPROBES > > config S390 > def_bool y > + select ADDR_LIMIT_CHECK > select ARCH_HAS_DEVMEM_IS_ALLOWED > select ARCH_HAS_ELF_RANDOMIZE > select ARCH_HAS_GCOV_PROFILE_ALL > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h > index 980c3c9b06f8..e534b93ce43a 100644 > --- a/include/linux/syscalls.h > +++ b/include/linux/syscalls.h > @@ -191,6 +191,28 @@ 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 addr_limit_check_syscall(void) > +{ > + BUG_ON(!segment_eq(get_fs(), USER_DS)); > +} > + > +#ifndef CONFIG_ADDR_LIMIT_CHECK > +#define ADDR_LIMIT_CHECK_PRE() \ > + bool user_caller = segment_eq(get_fs(), USER_DS) > +#define ADDR_LIMIT_CHECK_POST() \ > + if (user_caller) addr_limit_check_syscall() > +#else > +#define ADDR_LIMIT_CHECK_PRE() > +#define ADDR_LIMIT_CHECK_POST() > +asmlinkage void addr_limit_check_failed(void) __noreturn; > +#endif > + > + > #define __PROTECT(...) asmlinkage_protect(__VA_ARGS__) > #define __SYSCALL_DEFINEx(x, name, ...) \ > asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \ > @@ -199,7 +221,10 @@ 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; \ > + ADDR_LIMIT_CHECK_PRE(); \ > + ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \ > + ADDR_LIMIT_CHECK_POST(); \ > __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 42a346b0df43..599d9fe30703 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1961,6 +1961,12 @@ config PROFILING > config TRACEPOINTS > bool > > +config ADDR_LIMIT_CHECK > + bool > + help > + Disable the generic address limit check. 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 8a94b4eabcaa..a1cbcd715d62 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2458,3 +2458,16 @@ COMPAT_SYSCALL_DEFINE1(sysinfo, struct compat_sysinfo __user *, info) > return 0; > } > #endif /* CONFIG_COMPAT */ > + > +#ifdef CONFIG_ADDR_LIMIT_CHECK > +/* > + * Used when an architecture specific implementation detects an invalid address > + * limit. This function does not return. > + */ > +asmlinkage void addr_limit_check_failed(void) > +{ > + /* Try to fail on the generic address limit check */ > + addr_limit_check_syscall(); > + panic("Invalid address limit before returning to user-mode"); > +} > +#endif > -- > 2.13.0.rc0.306.g87b477812d-goog > -- Thomas