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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: Guo Ren <guoren@kernel.org>
Reviewed-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://lore.kernel.org/r/20221130023515.20217-2-palmer@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Palmer Dabbelt 2022-11-29 18:35:15 -08:00
parent b003b3b77d
commit de57ecc476
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1 changed files with 13 additions and 7 deletions
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20
arch/riscv/kernel/traps.c
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@ -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;