diff options
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/Kconfig | 23 | ||||
| -rw-r--r-- | arch/arm64/Kconfig | 1 | ||||
| -rw-r--r-- | arch/arm64/kernel/Makefile | 5 | ||||
| -rw-r--r-- | arch/arm64/kernel/syscall.c | 16 | ||||
| -rw-r--r-- | arch/x86/Kconfig | 1 | ||||
| -rw-r--r-- | arch/x86/entry/common.c | 3 | ||||
| -rw-r--r-- | arch/x86/include/asm/entry-common.h | 16 |
7 files changed, 65 insertions, 0 deletions
diff --git a/arch/Kconfig b/arch/Kconfig index ecfd3520b676..6b11c825fc36 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -1054,6 +1054,29 @@ config VMAP_STACK backing virtual mappings with real shadow memory, and KASAN_VMALLOC must be enabled. +config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET + def_bool n + help + An arch should select this symbol if it can support kernel stack + offset randomization with calls to add_random_kstack_offset() + during syscall entry and choose_random_kstack_offset() during + syscall exit. Careful removal of -fstack-protector-strong and + -fstack-protector should also be applied to the entry code and + closely examined, as the artificial stack bump looks like an array + to the compiler, so it will attempt to add canary checks regardless + of the static branch state. + +config RANDOMIZE_KSTACK_OFFSET_DEFAULT + bool "Randomize kernel stack offset on syscall entry" + depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET + help + The kernel stack offset can be randomized (after pt_regs) by + roughly 5 bits of entropy, frustrating memory corruption + attacks that depend on stack address determinism or + cross-syscall address exposures. This feature is controlled + by kernel boot param "randomize_kstack_offset=on/off", and this + config chooses the default boot state. + config ARCH_OPTIONAL_KERNEL_RWX def_bool n diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index dfdc3e0af5e1..f1a032ed2274 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -146,6 +146,7 @@ config ARM64 select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT select HAVE_ARCH_PFN_VALID select HAVE_ARCH_PREL32_RELOCATIONS + select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_STACKLEAK select HAVE_ARCH_THREAD_STRUCT_WHITELIST diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index ed65576ce710..6cc97730790e 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -9,6 +9,11 @@ CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_insn.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE) +# Remove stack protector to avoid triggering unneeded stack canary +# checks due to randomize_kstack_offset. +CFLAGS_REMOVE_syscall.o = -fstack-protector -fstack-protector-strong +CFLAGS_syscall.o += -fno-stack-protector + # Object file lists. obj-y := debug-monitors.o entry.o irq.o fpsimd.o \ entry-common.o entry-fpsimd.o process.o ptrace.o \ diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c index b9cf12b271d7..263d6c1a525f 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -5,6 +5,7 @@ #include <linux/errno.h> #include <linux/nospec.h> #include <linux/ptrace.h> +#include <linux/randomize_kstack.h> #include <linux/syscalls.h> #include <asm/daifflags.h> @@ -43,6 +44,8 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno, { long ret; + add_random_kstack_offset(); + if (scno < sc_nr) { syscall_fn_t syscall_fn; syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)]; @@ -55,6 +58,19 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno, ret = lower_32_bits(ret); regs->regs[0] = ret; + + /* + * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), + * but not enough for arm64 stack utilization comfort. To keep + * reasonable stack head room, reduce the maximum offset to 9 bits. + * + * The actual entropy will be further reduced by the compiler when + * applying stack alignment constraints: the AAPCS mandates a + * 16-byte (i.e. 4-bit) aligned SP at function boundaries. + * + * The resulting 5 bits of entropy is seen in SP[8:4]. + */ + choose_random_kstack_offset(get_random_int() & 0x1FF); } static inline bool has_syscall_work(unsigned long flags) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 6e0b08310949..f3db131be563 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -165,6 +165,7 @@ config X86 select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64 select HAVE_ARCH_USERFAULTFD_WP if X86_64 && USERFAULTFD select HAVE_ARCH_VMAP_STACK if X86_64 + select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET select HAVE_ARCH_WITHIN_STACK_FRAMES select HAVE_ASM_MODVERSIONS select HAVE_CMPXCHG_DOUBLE diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 4efd39aacb9f..7b2542b13ebd 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -38,6 +38,7 @@ #ifdef CONFIG_X86_64 __visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs) { + add_random_kstack_offset(); nr = syscall_enter_from_user_mode(regs, nr); instrumentation_begin(); @@ -83,6 +84,7 @@ __visible noinstr void do_int80_syscall_32(struct pt_regs *regs) { unsigned int nr = syscall_32_enter(regs); + add_random_kstack_offset(); /* * Subtlety here: if ptrace pokes something larger than 2^32-1 into * orig_ax, the unsigned int return value truncates it. This may @@ -102,6 +104,7 @@ static noinstr bool __do_fast_syscall_32(struct pt_regs *regs) unsigned int nr = syscall_32_enter(regs); int res; + add_random_kstack_offset(); /* * This cannot use syscall_enter_from_user_mode() as it has to * fetch EBP before invoking any of the syscall entry work diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h index 2b87b191b3b8..14ebd2196569 100644 --- a/arch/x86/include/asm/entry-common.h +++ b/arch/x86/include/asm/entry-common.h @@ -2,6 +2,7 @@ #ifndef _ASM_X86_ENTRY_COMMON_H #define _ASM_X86_ENTRY_COMMON_H +#include <linux/randomize_kstack.h> #include <linux/user-return-notifier.h> #include <asm/nospec-branch.h> @@ -70,6 +71,21 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs, */ current_thread_info()->status &= ~(TS_COMPAT | TS_I386_REGS_POKED); #endif + + /* + * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), + * but not enough for x86 stack utilization comfort. To keep + * reasonable stack head room, reduce the maximum offset to 8 bits. + * + * The actual entropy will be further reduced by the compiler when + * applying stack alignment constraints (see cc_stack_align4/8 in + * arch/x86/Makefile), which will remove the 3 (x86_64) or 2 (ia32) + * low bits from any entropy chosen here. + * + * Therefore, final stack offset entropy will be 5 (x86_64) or + * 6 (ia32) bits. + */ + choose_random_kstack_offset(rdtsc() & 0xFF); } #define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare |