From cabbf335824db0df835e4c541c19d3803ce38454 Mon Sep 17 00:00:00 2001 From: Kimplul Date: Wed, 14 Sep 2022 21:30:11 +0300 Subject: add canary to kernel stack --- common/canary.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) create mode 100644 common/canary.c (limited to 'common/canary.c') diff --git a/common/canary.c b/common/canary.c new file mode 100644 index 0000000..9fd89ff --- /dev/null +++ b/common/canary.c @@ -0,0 +1,39 @@ +#include +#include + +/** + * @file canary.c + * Kernel stack canary implementation. + */ + +/** Typedef for canary value type. */ +typedef uint32_t canary_t; + +/** Canary magic value. */ +static const canary_t canary = 0xb00b1e5; + +/** + * Helper for calculating the canary location of \p t. + * + * @param t \ref tcb to calculate canary position of. + * @return Pointer to canary location, that is bottom of stack. + * \todo This assumes that all stacks grow downwards. Unlikely to ever be + * ported to a platform that doesn't abide by this, but keep it in mind anyway. + */ +static canary_t *get_canary(struct tcb *t) +{ + size_t s = order_size(KERNEL_STACK_PAGE_ORDER); + return (canary_t *)align_down((uintptr_t)t, s); +} + +void set_canary(struct tcb *t) +{ + canary_t *c = get_canary(t); + *c = canary; +} + +bool check_canary(struct tcb *t) +{ + canary_t *c = get_canary(t); + return *c != canary; +} -- cgit v1.3