riscv: process: fix kernel info leakage

thread_struct's s[12] may contain random kernel memory content, which
may be finally leaked to userspace. This is a security hole. Fix it
by clearing the s[12] array in thread_struct when fork.

As for kthread case, it's better to clear the s[12] array as well.

Fixes: 7db91e57a0ac ("RISC-V: Task implementation")
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Tested-by: Guo Ren <guoren@kernel.org>
Link: https://lore.kernel.org/r/20221029113450.4027-1-jszhang@kernel.org
Reviewed-by: Guo Ren <guoren@kernel.org>
Link: https://lore.kernel.org/r/CAJF2gTSdVyAaM12T%2B7kXAdRPGS4VyuO08X1c7paE-n4Fr8OtRA@mail.gmail.com/
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index b0c63e8e867ef6979231d749ad98d2381d827a67..8955f2432c2d844c7e37b6ee69eea95ceffd7076 100644 (file)
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -164,6 +164,8 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
        unsigned long tls = args->tls;
        struct pt_regs *childregs = task_pt_regs(p);
 
+       memset(&p->thread.s, 0, sizeof(p->thread.s));
+
        /* p->thread holds context to be restored by __switch_to() */
        if (unlikely(args->fn)) {
                /* Kernel thread */