diff options
Diffstat (limited to 'drivers/misc/lkdtm/cfi.c')
| -rw-r--r-- | drivers/misc/lkdtm/cfi.c | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/drivers/misc/lkdtm/cfi.c b/drivers/misc/lkdtm/cfi.c new file mode 100644 index 000000000..fc28714ae --- /dev/null +++ b/drivers/misc/lkdtm/cfi.c @@ -0,0 +1,193 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * This is for all the tests relating directly to Control Flow Integrity. + */ +#include "lkdtm.h" +#include <asm/page.h> + +static int called_count; + +/* Function taking one argument, without a return value. */ +static noinline void lkdtm_increment_void(int *counter) +{ + (*counter)++; +} + +/* Function taking one argument, returning int. */ +static noinline int lkdtm_increment_int(int *counter) +{ + (*counter)++; + + return *counter; +} + +/* Don't allow the compiler to inline the calls. */ +static noinline void lkdtm_indirect_call(void (*func)(int *)) +{ + func(&called_count); +} + +/* + * This tries to call an indirect function with a mismatched prototype. + */ +static void lkdtm_CFI_FORWARD_PROTO(void) +{ + /* + * Matches lkdtm_increment_void()'s prototype, but not + * lkdtm_increment_int()'s prototype. + */ + pr_info("Calling matched prototype ...\n"); + lkdtm_indirect_call(lkdtm_increment_void); + + pr_info("Calling mismatched prototype ...\n"); + lkdtm_indirect_call((void *)lkdtm_increment_int); + + pr_err("FAIL: survived mismatched prototype function call!\n"); + pr_expected_config(CONFIG_CFI_CLANG); +} + +/* + * This can stay local to LKDTM, as there should not be a production reason + * to disable PAC && SCS. + */ +#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL +# ifdef CONFIG_ARM64_BTI_KERNEL +# define __no_pac "branch-protection=bti" +# else +# ifdef CONFIG_CC_HAS_BRANCH_PROT_PAC_RET +# define __no_pac "branch-protection=none" +# else +# define __no_pac "sign-return-address=none" +# endif +# endif +# define __no_ret_protection __noscs __attribute__((__target__(__no_pac))) +#else +# define __no_ret_protection __noscs +#endif + +#define no_pac_addr(addr) \ + ((__force __typeof__(addr))((uintptr_t)(addr) | PAGE_OFFSET)) + +/* The ultimate ROP gadget. */ +static noinline __no_ret_protection +void set_return_addr_unchecked(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 (no_pac_addr(*ret_addr) == expected) + *ret_addr = (addr); + else + /* Check architecture, stack layout, or compiler behavior... */ + pr_warn("Eek: return address mismatch! %px != %px\n", + *ret_addr, addr); +} + +static noinline +void set_return_addr(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 (no_pac_addr(*ret_addr) == expected) + *ret_addr = (addr); + else + /* Check architecture, stack layout, or compiler behavior... */ + pr_warn("Eek: return address mismatch! %px != %px\n", + *ret_addr, addr); +} + +static volatile int force_check; + +static void lkdtm_CFI_BACKWARD(void) +{ + /* Use calculated gotos to keep labels addressable. */ + void *labels[] = { NULL, &&normal, &&redirected, &&check_normal, &&check_redirected }; + + pr_info("Attempting unchecked stack return address redirection ...\n"); + + /* Always false */ + if (force_check) { + /* + * Prepare to call with NULLs to avoid parameters being treated as + * constants in -02. + */ + set_return_addr_unchecked(NULL, NULL); + set_return_addr(NULL, NULL); + if (force_check) + goto *labels[1]; + if (force_check) + goto *labels[2]; + if (force_check) + goto *labels[3]; + if (force_check) + goto *labels[4]; + return; + } + + /* + * Use fallthrough switch case to keep basic block ordering between + * set_return_addr*() and the label after it. + */ + switch (force_check) { + case 0: + set_return_addr_unchecked(&&normal, &&redirected); + fallthrough; + case 1: +normal: + /* Always true */ + if (!force_check) { + pr_err("FAIL: stack return address manipulation failed!\n"); + /* If we can't redirect "normally", we can't test mitigations. */ + return; + } + break; + default: +redirected: + pr_info("ok: redirected stack return address.\n"); + break; + } + + pr_info("Attempting checked stack return address redirection ...\n"); + + switch (force_check) { + case 0: + set_return_addr(&&check_normal, &&check_redirected); + fallthrough; + case 1: +check_normal: + /* Always true */ + if (!force_check) { + pr_info("ok: control flow unchanged.\n"); + return; + } + +check_redirected: + pr_err("FAIL: stack return address was redirected!\n"); + break; + } + + if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) { + pr_expected_config(CONFIG_ARM64_PTR_AUTH_KERNEL); + return; + } + if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK)) { + pr_expected_config(CONFIG_SHADOW_CALL_STACK); + return; + } + pr_warn("This is probably expected, since this %s was built *without* %s=y nor %s=y\n", + lkdtm_kernel_info, + "CONFIG_ARM64_PTR_AUTH_KERNEL", "CONFIG_SHADOW_CALL_STACK"); +} + +static struct crashtype crashtypes[] = { + CRASHTYPE(CFI_FORWARD_PROTO), + CRASHTYPE(CFI_BACKWARD), +}; + +struct crashtype_category cfi_crashtypes = { + .crashtypes = crashtypes, + .len = ARRAY_SIZE(crashtypes), +}; |