From 83e769b98e8e820cd1f58385a7f975b39d2087d6 Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Tue, 7 Jan 2025 12:02:11 -0800 Subject: [PATCH] Check for a missing `DT_HASH` section in the VDSO parser (#1254) * Check for a missing `DT_HASH` section in the VDSO parser Fix a missing check for a null hash table pointer, which can happen if the vDSO lacks a `DT_HASH` entry. Also, incorporate the changes in the latest upstream version of thee reference parse_vdso.c code. * Fix type differences on s390x. * Add more tests. * Remove an over-aggressive check. * Fix the name of getcpu on riscv64. FG: replace DT_GNU_HASH constant with value, can be removed once linux-raw-sys >= 0.6.6 is available in Debian Signed-off-by: Fabian Grünbichler --- src/backend/linux_raw/vdso.rs | 84 +++++++++++++++++++------- src/backend/linux_raw/vdso_wrappers.rs | 2 +- 2 files changed, 64 insertions(+), 22 deletions(-) --- a/src/backend/linux_raw/vdso.rs +++ b/src/backend/linux_raw/vdso.rs @@ -1,7 +1,7 @@ //! Parse the Linux vDSO. //! //! The following code is transliterated from -//! tools/testing/selftests/vDSO/parse_vdso.c in Linux 5.11, which is licensed +//! tools/testing/selftests/vDSO/parse_vdso.c in Linux 6.12, which is licensed //! with Creative Commons Zero License, version 1.0, //! available at //! @@ -20,6 +20,11 @@ use core::ptr::{null, null_mut}; use linux_raw_sys::elf::*; +#[cfg(target_arch = "s390x")] +type ElfHashEntry = u64; +#[cfg(not(target_arch = "s390x"))] +type ElfHashEntry = u32; + pub(super) struct Vdso { // Load information load_addr: *const Elf_Ehdr, @@ -29,17 +34,19 @@ // Symbol table symtab: *const Elf_Sym, symstrings: *const u8, - bucket: *const u32, - chain: *const u32, - nbucket: u32, - //nchain: u32, + bucket: *const ElfHashEntry, + chain: *const ElfHashEntry, + nbucket: ElfHashEntry, + //nchain: ElfHashEntry, // Version table versym: *const u16, verdef: *const Elf_Verdef, } -// Straight from the ELF specification. +/// Straight from the ELF specification...and then tweaked slightly, in order to +/// avoid a few clang warnings. +/// (And then translated to Rust). fn elf_hash(name: &CStr) -> u32 { let mut h: u32 = 0; for b in name.to_bytes() { @@ -91,11 +98,6 @@ 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. @@ -129,7 +131,7 @@ } // Fish out the useful bits of the dynamic table. - let mut hash: *const u32 = null(); + let mut hash: *const ElfHashEntry = null(); vdso.symstrings = null(); vdso.symtab = null(); vdso.versym = null(); @@ -152,8 +154,10 @@ .as_ptr(); } DT_HASH => { - hash = check_raw_pointer::(vdso.addr_from_elf(d.d_un.d_ptr)? as *mut _)? - .as_ptr(); + hash = check_raw_pointer::( + vdso.addr_from_elf(d.d_un.d_ptr)? as *mut _ + )? + .as_ptr(); } DT_VERSYM => { vdso.versym = @@ -176,8 +180,12 @@ } i = i.checked_add(1)?; } - // The upstream code checks `symstrings`, `symtab`, and `hash` for - // null; here, `check_raw_pointer` has already done that. + // `check_raw_pointer` will have checked these pointers for null, + // however they could still be null if the expected dynamic table + // entries are absent. + if vdso.symstrings.is_null() || vdso.symtab.is_null() || hash.is_null() { + return None; // Failed + } if vdso.verdef.is_null() { vdso.versym = null(); @@ -260,16 +268,20 @@ // SAFETY: The pointers in `self` must be valid. unsafe { - let mut chain = *self.bucket.add((name_hash % self.nbucket) as usize); + let mut chain = *self + .bucket + .add((ElfHashEntry::from(name_hash) % self.nbucket) as usize); - while chain != STN_UNDEF { + while chain != ElfHashEntry::from(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. + // Accept `STT_NOTYPE` in addition to `STT_FUNC` for the symbol + // type, for compatibility with some versions of Linux on + // PowerPC64. See [this commit] in Linux for more background. + // + // [this commit]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/tools/testing/selftests/vDSO/parse_vdso.c?id=0161bd38c24312853ed5ae9a425a1c41c4ac674a 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 @@ -311,3 +323,33 @@ self.base_plus(elf_addr.wrapping_add(self.pv_offset)) } } + +#[cfg(linux_raw)] +#[test] +#[ignore] // Until rustix is updated to the new vDSO format. +fn test_vdso() { + let vdso = Vdso::new().unwrap(); + assert!(!vdso.symtab.is_null()); + assert!(!vdso.symstrings.is_null()); + + #[cfg(target_arch = "x86_64")] + let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_gettime")); + #[cfg(target_arch = "arm")] + let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_gettime64")); + #[cfg(target_arch = "aarch64")] + let ptr = vdso.sym(cstr!("LINUX_2.6.39"), cstr!("__kernel_clock_gettime")); + #[cfg(target_arch = "x86")] + let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_gettime64")); + #[cfg(target_arch = "riscv64")] + let ptr = vdso.sym(cstr!("LINUX_4.15"), cstr!("__vdso_clock_gettime")); + #[cfg(target_arch = "powerpc64")] + let ptr = vdso.sym(cstr!("LINUX_2.6.15"), cstr!("__kernel_clock_gettime")); + #[cfg(target_arch = "s390x")] + let ptr = vdso.sym(cstr!("LINUX_2.6.29"), cstr!("__kernel_clock_gettime")); + #[cfg(any(target_arch = "mips", target_arch = "mips32r6"))] + let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_gettime64")); + #[cfg(any(target_arch = "mips64", target_arch = "mips64r6"))] + let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_gettime")); + + assert!(!ptr.is_null()); +} --- a/src/backend/linux_raw/vdso_wrappers.rs +++ b/src/backend/linux_raw/vdso_wrappers.rs @@ -556,7 +556,7 @@ #[cfg(target_arch = "x86")] let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_getcpu")); #[cfg(target_arch = "riscv64")] - let ptr = vdso.sym(cstr!("LINUX_4.15"), cstr!("__kernel_getcpu")); + let ptr = vdso.sym(cstr!("LINUX_4.15"), cstr!("__vdso_getcpu")); #[cfg(target_arch = "powerpc64")] let ptr = vdso.sym(cstr!("LINUX_2.6.15"), cstr!("__kernel_getcpu"));