veridian_kernel/mm/
user_validation.rs

1//! User space memory validation utilities
2//!
3//! Provides functions to validate user space addresses and check page mappings.
4
5use crate::mm::{
6    page_table::{PageTable, PageTableEntry},
7    PageFlags,
8};
9
10/// Check if a user address is valid (within user space range)
11pub fn is_user_addr_valid(addr: usize) -> bool {
12    // User space is 0x0 - 0x7FFF_FFFF_FFFF (128TB)
13    addr < 0x0000_8000_0000_0000
14}
15
16/// Translate a virtual address to its page table entry
17///
18/// Returns None if the address is not mapped
19pub fn translate_address(addr: usize) -> Option<PageTableEntry> {
20    // Get current process's page table
21    let _current_process = crate::process::current_process()?;
22
23    // Get the active page table base address (CR3 on x86_64).
24    // In VeridianOS, syscalls run with the process's page tables loaded
25    // (CR3 switching was removed from syscalls in v0.4.9 for performance).
26    // The kernel is mapped via L4[256-511] in every process's page table,
27    // so CR3 already points to the correct page table for translating both
28    // user and kernel addresses.
29    // SAFETY: get_kernel_page_table() returns the physical address of the
30    // active page table root. The page table memory is accessible via the
31    // kernel's physical memory mapping and has 'static lifetime.
32    let page_table = unsafe { &*(crate::mm::get_kernel_page_table() as *const PageTable) };
33
34    // Walk the page tables to find the entry
35    let vpn = addr >> 12; // Virtual page number
36
37    // 4-level page table walk (x86_64 style)
38    let l4_index = (vpn >> 27) & 0x1FF;
39    let l3_index = (vpn >> 18) & 0x1FF;
40    let l2_index = (vpn >> 9) & 0x1FF;
41    let l1_index = vpn & 0x1FF;
42
43    // Walk L4
44    let l4_entry = page_table[l4_index];
45    if !l4_entry.is_present() {
46        return None;
47    }
48
49    // Get L3 table
50    // SAFETY: l4_entry.addr() returns the physical address of the next-level
51    // page table. This address was set by the kernel's page table setup code
52    // and points to a valid PageTable in identity-mapped kernel memory.
53    let l3_table = unsafe { &*(l4_entry.addr()?.as_u64() as *const PageTable) };
54
55    let l3_entry = l3_table[l3_index];
56    if !l3_entry.is_present() {
57        return None;
58    }
59
60    // Check for huge page (1GB)
61    if l3_entry.flags().contains(PageFlags::HUGE) {
62        return Some(l3_entry);
63    }
64
65    // Get L2 table
66    // SAFETY: l3_entry.addr() returns the physical address of the next-level
67    // page table, set by kernel page table initialization. The address points
68    // to a valid PageTable in identity-mapped kernel memory.
69    let l2_table = unsafe { &*(l3_entry.addr()?.as_u64() as *const PageTable) };
70
71    let l2_entry = l2_table[l2_index];
72    if !l2_entry.is_present() {
73        return None;
74    }
75
76    // Check for large page (2MB)
77    if l2_entry.flags().contains(PageFlags::HUGE) {
78        return Some(l2_entry);
79    }
80
81    // Get L1 table
82    // SAFETY: l2_entry.addr() returns the physical address of the final-level
83    // page table, set by kernel page table initialization. The address points
84    // to a valid PageTable in identity-mapped kernel memory.
85    let l1_table = unsafe { &*(l2_entry.addr()?.as_u64() as *const PageTable) };
86
87    let l1_entry = l1_table[l1_index];
88    if !l1_entry.is_present() {
89        return None;
90    }
91
92    Some(l1_entry)
93}
94
95/// Extension trait for PageTableEntry to check user accessibility
96pub trait PageTableEntryExt {
97    fn is_user_accessible(&self) -> bool;
98}
99
100impl PageTableEntryExt for PageTableEntry {
101    fn is_user_accessible(&self) -> bool {
102        // Check user bit (bit 2) in flags
103        self.flags().contains(PageFlags::USER)
104    }
105}
veridian_kernel/mm/user_validation.rs

veridian_kernel/mm/
user_validation.rs
