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#include <kernel/arch/generic.h>
#include <kernel/mem.h>
#include <stdint.h>
/* <heat> nitpick: I highly recommend you dont use bitfields for paging
* structures
* <heat> you can't change them atomically and the way they're layed out
* in memory is implementation defined iirc
*/
struct pagetable_entry {
uint32_t present : 1;
uint32_t writeable : 1;
uint32_t user : 1;
uint32_t writethru : 1;
uint32_t uncached : 1;
uint32_t dirty : 1;
uint32_t always0 : 1; // memory type thing?
uint32_t global : 1;
uint32_t _unused : 3;
uint32_t address : 21;
};
struct pagedir_entry {
uint32_t present : 1;
uint32_t writeable : 1;
uint32_t user : 1;
uint32_t writethru : 1;
uint32_t uncached : 1;
uint32_t accessed : 1;
uint32_t always0 : 1;
uint32_t large : 1; // 4 MiB instead of 4 KiB
uint32_t _unused : 3;
uint32_t address : 21;
} __attribute__((packed));
struct pagedir {
struct pagedir_entry e[1024];
} __attribute__((packed));
struct pagedir *pagedir_new() {
struct pagedir *dir = page_alloc(1);
for (int i = 0; i < 1024; i++)
dir->e[i].present = 0;
return dir;
}
void pagedir_map(struct pagedir *dir, void *virt, void *phys,
bool user, bool writeable)
{
uintptr_t virt_casted = (uintptr_t) virt;
uint32_t pd_idx = virt_casted >> 22;
uint32_t pt_idx = virt_casted >> 12 & 0x03FF;
struct pagetable_entry *pagetable;
if (dir->e[pd_idx].present) {
pagetable = (void*) (dir->e[pd_idx].address << 11);
} else {
pagetable = page_alloc(1);
for (int i = 0; i < 1024; i++)
pagetable[i].present = 0;
dir->e[pd_idx] = (struct pagedir_entry) {
.present = 1,
.writeable = 1,
.user = 1,
.writethru = 1,
.uncached = 0,
.accessed = 0,
.always0 = 0,
.large = 0,
._unused = 0,
.address = (uintptr_t) pagetable >> 11
};
}
pagetable[pt_idx] = (struct pagetable_entry) {
.present = 1,
.writeable = writeable,
.user = user,
.writethru = 1,
.uncached = 0,
.dirty = 0,
.always0 = 0,
.global = 0,
._unused = 0,
.address = (uintptr_t) phys >> 11
};
}
void pagedir_switch(struct pagedir *dir) {
asm volatile("mov %0, %%cr3;" : : "r" (dir) : "memory");
}
void *pagedir_virt2phys(struct pagedir *dir, const void *virt,
bool user, bool writeable)
{
uintptr_t virt_casted = (uintptr_t) virt;
uintptr_t phys;
uint32_t pd_idx = virt_casted >> 22;
uint32_t pt_idx = virt_casted >> 12 & 0x03FF;
struct pagetable_entry *pagetable, page;
/* DOESN'T CHECK PERMISSIONS ON PAGE DIRS, TODO
* while i don't currently see a reason to set permissions
* directly on page dirs, i might see one in the future.
* leaving this as-is would be a security bug */
if (!dir->e[pd_idx].present) return 0;
pagetable = (void*)(dir->e[pd_idx].address << 11);
page = pagetable[pt_idx];
if (!page.present) return 0;
if (user && !page.user) return 0;
if (writeable && !page.writeable) return 0;
phys = page.address << 11;
phys |= (uintptr_t)virt & 0xFFF;
return (void*)phys;
}
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