__{get,put}_user calls are designed to be fast and have no checks,
relying on the caller to have made the appropriate calls previously.
It's very easy to forget a check though, leaving the kernel vulnerable
to exploits. Add an option to do the checks and kill the kernel if it
catches something bad.Signed-off-by: Laura Abbott <[email protected]> --- This is the actual implemtation for __{get,put}_user on x86 based on Mark Rutland's work for arm66 lkml.kernel.org/r/<[email protected]> x86 turns out to be easier since the safe and unsafe paths are mostly disjoint so we don't have to worry about gcc optimizing out access_ok. I tweaked the Kconfig to someting a bit more generic. The size increase was ~8K in text with a config I tested. --- arch/x86/Kconfig | 3 +++ arch/x86/include/asm/uaccess.h | 11 ++++++++++- security/Kconfig | 11 +++++++++++ 3 files changed, 24 insertions(+), 1 deletion(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 2fdb23313dd5..10c6e150a91e 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -261,6 +261,9 @@ config RWSEM_XCHGADD_ALGORITHM config GENERIC_CALIBRATE_DELAY def_bool y +config ARCH_HAS_PARANOID_UACCESS + def_bool y + config ARCH_HAS_CPU_RELAX def_bool y diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index d23fb5844404..767febe1c720 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -132,6 +132,13 @@ extern int __get_user_bad(void); #define __inttype(x) \ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) + +#define verify_uaccess(dir, ptr) \ +({ \ + if (IS_ENABLED(CONFIG_PARANOID_UACCESS)) \ + BUG_ON(!access_ok(dir, (ptr), sizeof(*(ptr)))); \ +}) + /** * get_user: - Get a simple variable from user space. * @x: Variable to store result. @@ -278,6 +285,7 @@ do { \ typeof(ptr) __pu_ptr = (ptr); \ retval = 0; \ __chk_user_ptr(__pu_ptr); \ + verify_uaccess(VERIFY_WRITE, __pu_ptr); \ switch (size) { \ case 1: \ __put_user_asm(x, __pu_ptr, retval, "b", "b", "iq", \ @@ -293,7 +301,7 @@ do { \ break; \ case 8: \ __put_user_asm_u64((__typeof__(*ptr))(x), __pu_ptr, \ - retval, \ errret); \ + retval, errret); \ break; \ default: \ __put_user_bad(); \ @@ -359,6 +367,7 @@ do { \ typeof(ptr) __gu_ptr = (ptr); \ retval = 0; \ __chk_user_ptr(__gu_ptr); \ + verify_uaccess(VERIFY_READ, __gu_ptr); \ switch (size) { \ case 1: \ __get_user_asm(x, __gu_ptr, retval, "b", "b", "=q", \ diff --git a/security/Kconfig b/security/Kconfig index e8e449444e65..0a9ec1a4e86b 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -205,6 +205,17 @@ config STATIC_USERMODEHELPER_PATH If you wish for all usermode helper programs to be disabled, specify an empty string here (i.e. ""). +config PARANOID_UACCESS + bool "Use paranoid uaccess primitives" + depends on ARCH_HAS_PARANOID_UACCESS + help + Forces access_ok() checks in __get_user(), __put_user(), and other + low-level uaccess primitives which usually do not have checks. This + can limit the effect of missing access_ok() checks in higher-level + primitives, with a runtime performance overhead in some cases and a + small code size overhead. + + source security/selinux/Kconfig source security/smack/Kconfig source security/tomoyo/Kconfig -- 2.13.5
