* Thomas Garnier <thgarnie@xxxxxxxxxx> 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. > > [1] https://bugs.chromium.org/p/project-zero/issues/detail?id=990 > > Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx> > Tested-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > 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..164de1d24e92 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 ADDR_LIMIT_CHECK > 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..ebde64f1622c 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 Ok, this version looks pretty good to me. Could you (re-)send a full series? I assume some of these changes need to be propagated into the followup patches but even if not it's better to pick up a clean series. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
