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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
commit | 2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch) | |
tree | 848558de17fb3008cdf4d861b01ac7781903ce39 /arch/x86/include/asm/stackprotector.h | |
parent | Initial commit. (diff) | |
download | linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip |
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'arch/x86/include/asm/stackprotector.h')
-rw-r--r-- | arch/x86/include/asm/stackprotector.h | 95 |
1 files changed, 95 insertions, 0 deletions
diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h new file mode 100644 index 000000000..24a8d6c4f --- /dev/null +++ b/arch/x86/include/asm/stackprotector.h @@ -0,0 +1,95 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * GCC stack protector support. + * + * Stack protector works by putting predefined pattern at the start of + * the stack frame and verifying that it hasn't been overwritten when + * returning from the function. The pattern is called stack canary + * and unfortunately gcc historically required it to be at a fixed offset + * from the percpu segment base. On x86_64, the offset is 40 bytes. + * + * The same segment is shared by percpu area and stack canary. On + * x86_64, percpu symbols are zero based and %gs (64-bit) points to the + * base of percpu area. The first occupant of the percpu area is always + * fixed_percpu_data which contains stack_canary at the appropriate + * offset. On x86_32, the stack canary is just a regular percpu + * variable. + * + * Putting percpu data in %fs on 32-bit is a minor optimization compared to + * using %gs. Since 32-bit userspace normally has %fs == 0, we are likely + * to load 0 into %fs on exit to usermode, whereas with percpu data in + * %gs, we are likely to load a non-null %gs on return to user mode. + * + * Once we are willing to require GCC 8.1 or better for 64-bit stackprotector + * support, we can remove some of this complexity. + */ + +#ifndef _ASM_STACKPROTECTOR_H +#define _ASM_STACKPROTECTOR_H 1 + +#ifdef CONFIG_STACKPROTECTOR + +#include <asm/tsc.h> +#include <asm/processor.h> +#include <asm/percpu.h> +#include <asm/desc.h> + +#include <linux/random.h> +#include <linux/sched.h> + +/* + * Initialize the stackprotector canary value. + * + * NOTE: this must only be called from functions that never return + * and it must always be inlined. + * + * In addition, it should be called from a compilation unit for which + * stack protector is disabled. Alternatively, the caller should not end + * with a function call which gets tail-call optimized as that would + * lead to checking a modified canary value. + */ +static __always_inline void boot_init_stack_canary(void) +{ + u64 canary; + u64 tsc; + +#ifdef CONFIG_X86_64 + BUILD_BUG_ON(offsetof(struct fixed_percpu_data, stack_canary) != 40); +#endif + /* + * We both use the random pool and the current TSC as a source + * of randomness. The TSC only matters for very early init, + * there it already has some randomness on most systems. Later + * on during the bootup the random pool has true entropy too. + */ + get_random_bytes(&canary, sizeof(canary)); + tsc = rdtsc(); + canary += tsc + (tsc << 32UL); + canary &= CANARY_MASK; + + current->stack_canary = canary; +#ifdef CONFIG_X86_64 + this_cpu_write(fixed_percpu_data.stack_canary, canary); +#else + this_cpu_write(__stack_chk_guard, canary); +#endif +} + +static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle) +{ +#ifdef CONFIG_X86_64 + per_cpu(fixed_percpu_data.stack_canary, cpu) = idle->stack_canary; +#else + per_cpu(__stack_chk_guard, cpu) = idle->stack_canary; +#endif +} + +#else /* STACKPROTECTOR */ + +/* dummy boot_init_stack_canary() is defined in linux/stackprotector.h */ + +static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle) +{ } + +#endif /* STACKPROTECTOR */ +#endif /* _ASM_STACKPROTECTOR_H */ |