diff options
Diffstat (limited to 'vendor/rustix/src/backend/linux_raw/vdso.rs')
| -rw-r--r-- | vendor/rustix/src/backend/linux_raw/vdso.rs | 313 |
1 files changed, 313 insertions, 0 deletions
diff --git a/vendor/rustix/src/backend/linux_raw/vdso.rs b/vendor/rustix/src/backend/linux_raw/vdso.rs new file mode 100644 index 0000000..102fa6b --- /dev/null +++ b/vendor/rustix/src/backend/linux_raw/vdso.rs @@ -0,0 +1,313 @@ +//! Parse the Linux vDSO. +//! +//! The following code is transliterated from +//! tools/testing/selftests/vDSO/parse_vdso.c in Linux 5.11, which is licensed +//! with Creative Commons Zero License, version 1.0, +//! available at <https://creativecommons.org/publicdomain/zero/1.0/legalcode> +//! +//! # Safety +//! +//! Parsing the vDSO involves a lot of raw pointer manipulation. This +//! implementation follows Linux's reference implementation, and adds several +//! additional safety checks. +#![allow(unsafe_code)] + +use super::c; +use crate::ffi::CStr; +use crate::utils::check_raw_pointer; +use core::ffi::c_void; +use core::mem::size_of; +use core::ptr::{null, null_mut}; +use linux_raw_sys::elf::*; + +pub(super) struct Vdso { + // Load information + load_addr: *const Elf_Ehdr, + load_end: *const c_void, // the end of the `PT_LOAD` segment + pv_offset: usize, // recorded paddr - recorded vaddr + + // Symbol table + symtab: *const Elf_Sym, + symstrings: *const u8, + bucket: *const u32, + chain: *const u32, + nbucket: u32, + //nchain: u32, + + // Version table + versym: *const u16, + verdef: *const Elf_Verdef, +} + +// Straight from the ELF specification. +fn elf_hash(name: &CStr) -> u32 { + let mut h: u32 = 0; + for b in name.to_bytes() { + h = (h << 4).wrapping_add(u32::from(*b)); + let g = h & 0xf000_0000; + if g != 0 { + h ^= g >> 24; + } + h &= !g; + } + h +} + +/// Create a `Vdso` value by parsing the vDSO at the `sysinfo_ehdr` address. +fn init_from_sysinfo_ehdr() -> Option<Vdso> { + // SAFETY: The auxv initialization code does extensive checks to ensure + // that the value we get really is an `AT_SYSINFO_EHDR` value from the + // kernel. + unsafe { + let hdr = super::param::auxv::sysinfo_ehdr(); + + // If the platform doesn't provide a `AT_SYSINFO_EHDR`, we can't locate + // the vDSO. + if hdr.is_null() { + return None; + } + + let mut vdso = Vdso { + load_addr: hdr, + load_end: hdr.cast(), + pv_offset: 0, + symtab: null(), + symstrings: null(), + bucket: null(), + chain: null(), + nbucket: 0, + //nchain: 0, + versym: null(), + verdef: null(), + }; + + let hdr = &*hdr; + let pt = check_raw_pointer::<Elf_Phdr>(vdso.base_plus(hdr.e_phoff)? as *mut _)?.as_ptr(); + let mut dyn_: *const Elf_Dyn = null(); + let mut num_dyn = 0; + + // We need two things from the segment table: the load offset + // and the dynamic table. + let mut found_vaddr = false; + for i in 0..hdr.e_phnum { + let phdr = &*pt.add(i as usize); + if phdr.p_flags & PF_W != 0 { + // Don't trust any vDSO that claims to be loading writable + // segments into memory. + return None; + } + if phdr.p_type == PT_LOAD && !found_vaddr { + // The segment should be readable and executable, because it + // contains the symbol table and the function bodies. + if phdr.p_flags & (PF_R | PF_X) != (PF_R | PF_X) { + return None; + } + found_vaddr = true; + vdso.load_end = vdso.base_plus(phdr.p_offset.checked_add(phdr.p_memsz)?)?; + vdso.pv_offset = phdr.p_offset.wrapping_sub(phdr.p_vaddr); + } else if phdr.p_type == PT_DYNAMIC { + // If `p_offset` is zero, it's more likely that we're looking + // at memory that has been zeroed than that the kernel has + // somehow aliased the `Ehdr` and the `Elf_Dyn` array. + if phdr.p_offset < size_of::<Elf_Ehdr>() { + return None; + } + + dyn_ = check_raw_pointer::<Elf_Dyn>(vdso.base_plus(phdr.p_offset)? as *mut _)? + .as_ptr(); + num_dyn = phdr.p_memsz / size_of::<Elf_Dyn>(); + } else if phdr.p_type == PT_INTERP || phdr.p_type == PT_GNU_RELRO { + // Don't trust any ELF image that has an “interpreter” or + // that uses RELRO, which is likely to be a user ELF image + // rather and not the kernel vDSO. + return None; + } + } + + if !found_vaddr || dyn_.is_null() { + return None; // Failed + } + + // Fish out the useful bits of the dynamic table. + let mut hash: *const u32 = null(); + vdso.symstrings = null(); + vdso.symtab = null(); + vdso.versym = null(); + vdso.verdef = null(); + let mut i = 0; + loop { + if i == num_dyn { + return None; + } + let d = &*dyn_.add(i); + match d.d_tag { + DT_STRTAB => { + vdso.symstrings = + check_raw_pointer::<u8>(vdso.addr_from_elf(d.d_un.d_ptr)? as *mut _)? + .as_ptr(); + } + DT_SYMTAB => { + vdso.symtab = + check_raw_pointer::<Elf_Sym>(vdso.addr_from_elf(d.d_un.d_ptr)? as *mut _)? + .as_ptr(); + } + DT_HASH => { + hash = check_raw_pointer::<u32>(vdso.addr_from_elf(d.d_un.d_ptr)? as *mut _)? + .as_ptr(); + } + DT_VERSYM => { + vdso.versym = + check_raw_pointer::<u16>(vdso.addr_from_elf(d.d_un.d_ptr)? as *mut _)? + .as_ptr(); + } + DT_VERDEF => { + vdso.verdef = check_raw_pointer::<Elf_Verdef>( + vdso.addr_from_elf(d.d_un.d_ptr)? as *mut _, + )? + .as_ptr(); + } + DT_SYMENT => { + if d.d_un.d_ptr != size_of::<Elf_Sym>() { + return None; // Failed + } + } + DT_NULL => break, + _ => {} + } + i = i.checked_add(1)?; + } + // The upstream code checks `symstrings`, `symtab`, and `hash` for + // null; here, `check_raw_pointer` has already done that. + + if vdso.verdef.is_null() { + vdso.versym = null(); + } + + // Parse the hash table header. + vdso.nbucket = *hash.add(0); + //vdso.nchain = *hash.add(1); + vdso.bucket = hash.add(2); + vdso.chain = hash.add(vdso.nbucket as usize + 2); + + // That's all we need. + Some(vdso) + } +} + +impl Vdso { + /// Parse the vDSO. + /// + /// Returns `None` if the vDSO can't be located or if it doesn't conform to + /// our expectations. + #[inline] + pub(super) fn new() -> Option<Self> { + init_from_sysinfo_ehdr() + } + + /// Check the version for a symbol. + /// + /// # Safety + /// + /// The raw pointers inside `self` must be valid. + unsafe fn match_version(&self, mut ver: u16, name: &CStr, hash: u32) -> bool { + // This is a helper function to check if the version indexed by + // ver matches name (which hashes to hash). + // + // The version definition table is a mess, and I don't know how + // to do this in better than linear time without allocating memory + // to build an index. I also don't know why the table has + // variable size entries in the first place. + // + // For added fun, I can't find a comprehensible specification of how + // to parse all the weird flags in the table. + // + // So I just parse the whole table every time. + + // First step: find the version definition + ver &= 0x7fff; // Apparently bit 15 means "hidden" + let mut def = self.verdef; + loop { + if (*def).vd_version != VER_DEF_CURRENT { + return false; // Failed + } + + if ((*def).vd_flags & VER_FLG_BASE) == 0 && ((*def).vd_ndx & 0x7fff) == ver { + break; + } + + if (*def).vd_next == 0 { + return false; // No definition. + } + + def = def + .cast::<u8>() + .add((*def).vd_next as usize) + .cast::<Elf_Verdef>(); + } + + // Now figure out whether it matches. + let aux = &*(def.cast::<u8>()) + .add((*def).vd_aux as usize) + .cast::<Elf_Verdaux>(); + (*def).vd_hash == hash + && (name == CStr::from_ptr(self.symstrings.add(aux.vda_name as usize).cast())) + } + + /// Look up a symbol in the vDSO. + pub(super) fn sym(&self, version: &CStr, name: &CStr) -> *mut c::c_void { + let ver_hash = elf_hash(version); + let name_hash = elf_hash(name); + + // SAFETY: The pointers in `self` must be valid. + unsafe { + let mut chain = *self.bucket.add((name_hash % self.nbucket) as usize); + + while chain != STN_UNDEF { + let sym = &*self.symtab.add(chain as usize); + + // Check for a defined global or weak function w/ right name. + // + // The reference parser in Linux's parse_vdso.c requires + // symbols to have type `STT_FUNC`, but on powerpc64, the vDSO + // uses `STT_NOTYPE`, so allow that too. + if (ELF_ST_TYPE(sym.st_info) != STT_FUNC && + ELF_ST_TYPE(sym.st_info) != STT_NOTYPE) + || (ELF_ST_BIND(sym.st_info) != STB_GLOBAL + && ELF_ST_BIND(sym.st_info) != STB_WEAK) + || sym.st_shndx == SHN_UNDEF + || sym.st_shndx == SHN_ABS + || ELF_ST_VISIBILITY(sym.st_other) != STV_DEFAULT + || (name != CStr::from_ptr(self.symstrings.add(sym.st_name as usize).cast())) + // Check symbol version. + || (!self.versym.is_null() + && !self.match_version(*self.versym.add(chain as usize), version, ver_hash)) + { + chain = *self.chain.add(chain as usize); + continue; + } + + let sum = self.addr_from_elf(sym.st_value).unwrap(); + assert!( + sum as usize >= self.load_addr as usize + && sum as usize <= self.load_end as usize + ); + return sum as *mut c::c_void; + } + } + + null_mut() + } + + /// Add the given address to the vDSO base address. + unsafe fn base_plus(&self, offset: usize) -> Option<*const c_void> { + // Check for overflow. + let _ = (self.load_addr as usize).checked_add(offset)?; + // Add the offset to the base. + Some(self.load_addr.cast::<u8>().add(offset).cast()) + } + + /// Translate an ELF-address-space address into a usable virtual address. + unsafe fn addr_from_elf(&self, elf_addr: usize) -> Option<*const c_void> { + self.base_plus(elf_addr.wrapping_add(self.pv_offset)) + } +} |