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Make translate_addr unsafe (#544)

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This function casts a usize argument to a pointer, and dereferences it.
This is undefined behavior unless level_4_table_addr is the address of a
valid PageTable, so the function should be marked 'unsafe'
This commit is contained in:
Aaron Hill
2019-02-01 06:39:14 -05:00
committed by Philipp Oppermann
parent b9ff59fd75
commit 0c5e303175
1 changed files with 13 additions and 8 deletions
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21
blog/content/second-edition/posts/10-advanced-paging/index.md
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@@ -180,7 +180,10 @@ use x86_64::structures::paging::PageTable;
/// Returns the physical address for the given virtual address, or `None` if the
/// virtual address is not mapped.
pub fn translate_addr(addr: usize, level_4_table_addr: usize) -> Option<PhysAddr> {
///
/// Safety: This requires level_4_table_addr to be the address of a valid
/// level-4 PageTable
pub unsafe fn translate_addr(addr: usize, level_4_table_addr: usize) -> Option<PhysAddr> {
// retrieve the page table indices of the address that we want to translate
let level_4_index = (addr >> 39) & 0o777;
let level_3_index = (addr >> 30) & 0o777;
@@ -252,13 +255,15 @@ pub extern "C" fn _start() -> ! {
const LEVEL_4_TABLE_ADDR: usize = 0o_177777_777_777_777_777_0000;
// the identity-mapped vga buffer page
println!("0xb8000 -> {:?}", translate_addr(0xb8000, LEVEL_4_TABLE_ADDR));
// some code page
println!("0x20010a -> {:?}", translate_addr(0x20010a, LEVEL_4_TABLE_ADDR));
// some stack page
println!("0x57ac001ffe48 -> {:?}", translate_addr(0x57ac001ffe48,
LEVEL_4_TABLE_ADDR));
unsafe {
// the identity-mapped vga buffer page
println!("0xb8000 -> {:?}", translate_addr(0xb8000, LEVEL_4_TABLE_ADDR));
// some code page
println!("0x20010a -> {:?}", translate_addr(0x20010a, LEVEL_4_TABLE_ADDR));
// some stack page
println!("0x57ac001ffe48 -> {:?}", translate_addr(0x57ac001ffe48,
LEVEL_4_TABLE_ADDR));
}
println!("It did not crash!");
blog_os::hlt_loop();