While almost all users of shadow stacks should be relying on the dynamic linker and libc to enable the feature there are several low level test programs where it is useful to enable without any libc support, allowing testing without full system enablement. This low level testing is helpful during bringup of the support itself, and also in enabling coverage by automated testing without needing all system components in the target root filesystems to have enablement.
Provide a header with helpers for this purpose, intended for use only by test programs directly exercising shadow stack interfaces.
Reviewed-by: Rick Edgecombe rick.p.edgecombe@intel.com Signed-off-by: Mark Brown broonie@kernel.org --- tools/testing/selftests/ksft_shstk.h | 63 ++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+)
diff --git a/tools/testing/selftests/ksft_shstk.h b/tools/testing/selftests/ksft_shstk.h new file mode 100644 index 000000000000..85d0747c1802 --- /dev/null +++ b/tools/testing/selftests/ksft_shstk.h @@ -0,0 +1,63 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Helpers for shadow stack enablement, this is intended to only be + * used by low level test programs directly exercising interfaces for + * working with shadow stacks. + * + * Copyright (C) 2024 ARM Ltd. + */ + +#ifndef __KSFT_SHSTK_H +#define __KSFT_SHSTK_H + +#include <asm/mman.h> + +/* This is currently only defined for x86 */ +#ifndef SHADOW_STACK_SET_TOKEN +#define SHADOW_STACK_SET_TOKEN (1ULL << 0) +#endif + +static bool shadow_stack_enabled; + +#ifdef __x86_64__ +#define ARCH_SHSTK_ENABLE 0x5001 +#define ARCH_SHSTK_SHSTK (1ULL << 0) + +#define ARCH_PRCTL(arg1, arg2) \ +({ \ + long _ret; \ + register long _num asm("eax") = __NR_arch_prctl; \ + register long _arg1 asm("rdi") = (long)(arg1); \ + register long _arg2 asm("rsi") = (long)(arg2); \ + \ + asm volatile ( \ + "syscall\n" \ + : "=a"(_ret) \ + : "r"(_arg1), "r"(_arg2), \ + "0"(_num) \ + : "rcx", "r11", "memory", "cc" \ + ); \ + _ret; \ +}) + +#define ENABLE_SHADOW_STACK +static inline __attribute__((always_inline)) void enable_shadow_stack(void) +{ + int ret = ARCH_PRCTL(ARCH_SHSTK_ENABLE, ARCH_SHSTK_SHSTK); + if (ret == 0) + shadow_stack_enabled = true; +} + +#endif + +#ifndef __NR_map_shadow_stack +#define __NR_map_shadow_stack 453 +#endif + +#ifndef ENABLE_SHADOW_STACK +static inline void enable_shadow_stack(void) { } +#endif + +#endif + +