Hi Kees,
Gentile ping for this :).
I also saw the discussion on llvm-project, use address of labels as a parameter doesn't seem to be stable.
Do we need to split it into two cases here?
Link: https://github.com/llvm/llvm-project/issues/54328
Thanks, Dan
On 3/14/22 06:53, Dan Li wrote:
Add tests for SCS (Shadow Call Stack) based backward CFI.
Signed-off-by: Dan Li ashimida@linux.alibaba.com
arch/arm64/include/asm/compiler.h | 18 ++++++ drivers/misc/lkdtm/cfi.c | 84 +++++++++++++++++++++++++ drivers/misc/lkdtm/core.c | 1 + drivers/misc/lkdtm/lkdtm.h | 1 + include/linux/compiler-clang.h | 1 + include/linux/compiler-gcc.h | 2 + include/linux/compiler_types.h | 4 ++ tools/testing/selftests/lkdtm/tests.txt | 1 + 8 files changed, 112 insertions(+)
diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h index dc3ea4080e2e..96590fb4a8de 100644 --- a/arch/arm64/include/asm/compiler.h +++ b/arch/arm64/include/asm/compiler.h @@ -8,6 +8,24 @@ #define ARM64_ASM_PREAMBLE #endif +#ifndef __ASSEMBLY__ +#ifdef __KERNEL__
+#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
+#ifdef CONFIG_ARM64_BTI_KERNEL +# define __no_ptrauth __attribute__((target("branch-protection=bti"))) +#elif defined(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) +# define __no_ptrauth __attribute__((target("branch-protection=none"))) +#elif defined(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) +# define __no_ptrauth __attribute__((target("sign-return-address=none"))) +#endif
+#endif /* CONFIG_ARM64_PTR_AUTH_KERNEL */
+#endif /* __KERNEL__ */ +#endif /* __ASSEMBLY__ */
- /*
- The EL0/EL1 pointer bits used by a pointer authentication code.
- This is dependent on TBI0/TBI1 being enabled, or bits 63:56 would also apply.
diff --git a/drivers/misc/lkdtm/cfi.c b/drivers/misc/lkdtm/cfi.c index c9aeddef1044..468ba2f26f74 100644 --- a/drivers/misc/lkdtm/cfi.c +++ b/drivers/misc/lkdtm/cfi.c @@ -41,3 +41,87 @@ void lkdtm_CFI_FORWARD_PROTO(void) pr_err("FAIL: survived mismatched prototype function call!\n"); pr_expected_config(CONFIG_CFI_CLANG); }
+#ifdef CONFIG_ARM64 +/*
- This function is used to modify its return address. The PAC needs to be turned
- off here to ensure that the modification of the return address will not be blocked.
- */
+static noinline __no_ptrauth +void lkdtm_scs_set_lr(unsigned long *expected, unsigned long *addr) +{
- /* Use of volatile is to make sure final write isn't seen as a dead store. */
- unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1;
- /* Make sure we've found the right place on the stack before writing it. */
- if (*ret_addr == expected)
*ret_addr = addr;+}
+/* Function with __noscs attribute attempts to modify its return address. */ +static noinline __no_ptrauth __noscs +void lkdtm_noscs_set_lr(unsigned long *expected, unsigned long *addr) +{
- /* Use of volatile is to make sure final write isn't seen as a dead store. */
- unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1;
- /* Make sure we've found the right place on the stack before writing it. */
- if (*ret_addr == expected)
*ret_addr = addr;+} +#else +static inline void lkdtm_noscs_set_lr(unsigned long *expected, unsigned long *addr) { } +static inline void lkdtm_scs_set_lr(unsigned long *expected, unsigned long *addr) { } +#endif
+static volatile unsigned int force_label;
+/*
- This first checks whether a function with the __noscs attribute under
- the current platform can directly modify its return address, and if so,
- checks whether scs takes effect.
- */
+void __no_optimize lkdtm_CFI_BACKWARD_SHADOW(void) +{
- void *array[] = {&&unexpected, &&expected, &&good_scs, &&bad_scs};
- if (force_label && (force_label < sizeof(array))) {
/** Call them with "NULL" first to avoid* arguments being treated as constants in -02.*/lkdtm_noscs_set_lr(NULL, NULL);lkdtm_scs_set_lr(NULL, NULL);goto *array[force_label];- }
- /* Keep labels in scope to avoid compiler warnings. */
- do {
/* Verify the "normal" condition of LR corruption working. */pr_info("Trying to corrupt lr in a function without scs protection ...\n");lkdtm_noscs_set_lr(&&unexpected, &&expected);+unexpected:
/** If lr cannot be modified, the following check is meaningless,* returns directly.*/pr_err("XPASS: Unexpectedly survived lr corruption without scs?!\n");break;+expected:
pr_info("ok: lr corruption redirected without scs.\n");/* Verify that SCS is in effect. */pr_info("Trying to corrupt lr in a function with scs protection ...\n");lkdtm_scs_set_lr(&&good_scs, &&bad_scs);+good_scs:
pr_info("ok: scs takes effect.\n");break;+bad_scs:
pr_err("FAIL: return address rewritten!\n");pr_expected_config(CONFIG_SHADOW_CALL_STACK);- } while (0);
+} diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c index f69b964b9952..7af7268b82e4 100644 --- a/drivers/misc/lkdtm/core.c +++ b/drivers/misc/lkdtm/core.c @@ -178,6 +178,7 @@ static const struct crashtype crashtypes[] = { CRASHTYPE(USERCOPY_KERNEL), CRASHTYPE(STACKLEAK_ERASING), CRASHTYPE(CFI_FORWARD_PROTO),
- CRASHTYPE(CFI_BACKWARD_SHADOW), CRASHTYPE(FORTIFIED_OBJECT), CRASHTYPE(FORTIFIED_SUBOBJECT), CRASHTYPE(FORTIFIED_STRSCPY),
diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h index d6137c70ebbe..a66fba949ab5 100644 --- a/drivers/misc/lkdtm/lkdtm.h +++ b/drivers/misc/lkdtm/lkdtm.h @@ -157,6 +157,7 @@ void lkdtm_STACKLEAK_ERASING(void); /* cfi.c */ void lkdtm_CFI_FORWARD_PROTO(void); +void lkdtm_CFI_BACKWARD_SHADOW(void); /* fortify.c */ void lkdtm_FORTIFIED_OBJECT(void); diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index 3c4de9b6c6e3..2db37db36651 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -68,3 +68,4 @@ #define __nocfi __attribute__((__no_sanitize__("cfi"))) #define __cficanonical __attribute__((__cfi_canonical_jump_table__)) +#define __no_optimize __attribute__((optnone)) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index deff5b308470..28d1b0ec6656 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -162,3 +162,5 @@ #if GCC_VERSION < 90100 #undef __alloc_size__ #endif
+#define __no_optimize __attribute__((optimize("-O0"))) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 3c1795fdb568..f5ad83f7ea2f 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -257,6 +257,10 @@ struct ftrace_likely_data { # define __nocfi #endif +#ifndef __no_ptrauth +# define __no_ptrauth +#endif
- #ifndef __cficanonical # define __cficanonical #endif
diff --git a/tools/testing/selftests/lkdtm/tests.txt b/tools/testing/selftests/lkdtm/tests.txt index 6b36b7f5dcf9..12df67a3b419 100644 --- a/tools/testing/selftests/lkdtm/tests.txt +++ b/tools/testing/selftests/lkdtm/tests.txt @@ -73,6 +73,7 @@ USERCOPY_STACK_BEYOND USERCOPY_KERNEL STACKLEAK_ERASING OK: the rest of the thread stack is properly erased CFI_FORWARD_PROTO +CFI_BACKWARD_SHADOW ok: scs takes effect FORTIFIED_STRSCPY FORTIFIED_OBJECT FORTIFIED_SUBOBJECT