Unverified Commit de57ecc4 authored by Palmer Dabbelt's avatar Palmer Dabbelt
Browse files

RISC-V: Add some comments about the shadow and overflow stacks 



It took me a while to page all this back in when trying to review the
recent spin_shadow_stack, so I figured I'd just write up some comments.

Reviewed-by: default avatarGuo Ren <guoren@kernel.org>
Reviewed-by: default avatarJisheng Zhang <jszhang@kernel.org>
Link: https://lore.kernel.org/r/20221130023515.20217-2-palmer@rivosinc.com


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent b003b3b7

arch/riscv/kernel/traps.c

+13 −7
Original line number Diff line number Diff line
@@ -200,18 +200,18 @@ void __init trap_init(void) 
}



#ifdef CONFIG_VMAP_STACK

/*

 * Extra stack space that allows us to provide panic messages when the kernel

 * has overflowed its stack.

 */

static DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)],

		overflow_stack)__aligned(16);

/*

 * shadow stack, handled_ kernel_ stack_ overflow(in kernel/entry.S) is used

 * to get per-cpu overflow stack(get_overflow_stack).

 * A temporary stack for use by handle_kernel_stack_overflow.  This is used so

 * we can call into C code to get the per-hart overflow stack.  Usage of this

 * stack must be protected by spin_shadow_stack.

 */

long shadow_stack[SHADOW_OVERFLOW_STACK_SIZE/sizeof(long)] __aligned(16);

asmlinkage unsigned long get_overflow_stack(void)

{

	return (unsigned long)this_cpu_ptr(overflow_stack) +

		OVERFLOW_STACK_SIZE;

}



/*

 * A pseudo spinlock to protect the shadow stack from being used by multiple
@@ -222,6 +222,12 @@ asmlinkage unsigned long get_overflow_stack(void) 
 */

unsigned long spin_shadow_stack;



asmlinkage unsigned long get_overflow_stack(void)

{

	return (unsigned long)this_cpu_ptr(overflow_stack) +

		OVERFLOW_STACK_SIZE;

}



asmlinkage void handle_bad_stack(struct pt_regs *regs)

{

	unsigned long tsk_stk = (unsigned long)current->stack;