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From 83e769b98e8e820cd1f58385a7f975b39d2087d6 Mon Sep 17 00:00:00 2001
From: Dan Gohman <dev@sunfishcode.online>
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 <debian@fabian.gruenbichler.email>
---
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 <https://creativecommons.org/publicdomain/zero/1.0/legalcode>
//!
@@ -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::<u32>(vdso.addr_from_elf(d.d_un.d_ptr)? as *mut _)?
- .as_ptr();
+ hash = check_raw_pointer::<ElfHashEntry>(
+ 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"));
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