diff options
| author | Song Shuai <songshuaishuai@tinylab.org> | 2023-11-09 21:37:51 +0800 |
|---|---|---|
| committer | Palmer Dabbelt <palmer@rivosinc.com> | 2024-01-24 17:24:24 -0800 |
| commit | 05d450aabd7386246c5aafc341fe9febe5855967 (patch) | |
| tree | a1634b1c6849df1e263bdf3fcceff904d9d14fbb /arch/riscv/kernel/traps.c | |
| parent | dded618c07fd786f781c3f3529d8253e31e2c7d6 (diff) | |
riscv: Support RANDOMIZE_KSTACK_OFFSET
Inspired from arm64's implement -- commit 70918779aec9
("arm64: entry: Enable random_kstack_offset support")
Add support of kernel stack offset randomization while handling syscall,
the offset is defaultly limited by KSTACK_OFFSET_MAX() (i.e. 10 bits).
In order to avoid trigger stack canaries (due to __builtin_alloca) and
slowing down the entry path, use __no_stack_protector attribute to
disable stack protector for do_trap_ecall_u() at the function level.
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Song Shuai <songshuaishuai@tinylab.org>
Link: https://lore.kernel.org/r/20231109133751.212079-1-songshuaishuai@tinylab.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Diffstat (limited to 'arch/riscv/kernel/traps.c')
| -rw-r--r-- | arch/riscv/kernel/traps.c | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index a1b9be3c4332..868d6280cf66 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -6,6 +6,7 @@ #include <linux/cpu.h> #include <linux/kernel.h> #include <linux/init.h> +#include <linux/randomize_kstack.h> #include <linux/sched.h> #include <linux/sched/debug.h> #include <linux/sched/signal.h> @@ -310,7 +311,8 @@ asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs) } } -asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs) +asmlinkage __visible __trap_section __no_stack_protector +void do_trap_ecall_u(struct pt_regs *regs) { if (user_mode(regs)) { long syscall = regs->a7; @@ -322,10 +324,23 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs) syscall = syscall_enter_from_user_mode(regs, syscall); + add_random_kstack_offset(); + if (syscall >= 0 && syscall < NR_syscalls) syscall_handler(regs, syscall); else if (syscall != -1) regs->a0 = -ENOSYS; + /* + * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), + * so the maximum stack offset is 1k bytes (10 bits). + * + * The actual entropy will be further reduced by the compiler when + * applying stack alignment constraints: 16-byte (i.e. 4-bit) aligned + * for RV32I or RV64I. + * + * The resulting 6 bits of entropy is seen in SP[9:4]. + */ + choose_random_kstack_offset(get_random_u16()); syscall_exit_to_user_mode(regs); } else { |