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Implement the DT_GNU_HASH mechanism for vDSO parsing. #1259

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Merged
merged 5 commits into from
Jan 13, 2025
Merged

Implement the DT_GNU_HASH mechanism for vDSO parsing. #1259

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67e0afb
Implement the `DT_GNU_HASH` mechanism for vDSO parsing.
sunfishcode Jan 8, 2025
e9dbd57
Fix compilation on s390x with experimental asm.
sunfishcode Jan 8, 2025
b400014
Fix pointer arithmetic on s390x.
sunfishcode Jan 8, 2025
05e7835
Add comments.
sunfishcode Jan 8, 2025
515b2c8
Add more vDSO tests, and enable vDSO getcpu on s390x.
sunfishcode Jan 8, 2025
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6 changes: 4 additions & 2 deletions src/backend/linux_raw/process/syscalls.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,8 @@ use {crate::backend::conv::slice_just_addr_mut, crate::process::Gid};
target_arch = "x86_64",
target_arch = "x86",
target_arch = "riscv64",
target_arch = "powerpc64"
target_arch = "powerpc64",
target_arch = "s390x"
))]
pub(crate) use crate::backend::vdso_wrappers::sched_getcpu;

Expand All @@ -50,7 +51,8 @@ pub(crate) use crate::backend::vdso_wrappers::sched_getcpu;
target_arch = "x86_64",
target_arch = "x86",
target_arch = "riscv64",
target_arch = "powerpc64"
target_arch = "powerpc64",
target_arch = "s390x"
)))]
#[inline]
pub(crate) fn sched_getcpu() -> usize {
Expand Down
291 changes: 229 additions & 62 deletions src/backend/linux_raw/vdso.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,10 @@
//! with Creative Commons Zero License, version 1.0,
//! available at <https://creativecommons.org/publicdomain/zero/1.0/legalcode>
//!
//! It also incorporates the patch at:
//! <https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git/commit/tools/testing/selftests/vDSO?h=next&id=01587d80b04f29747b6fd6d766c3bfa632f14eb0>,
//! with changes to fix the pointer arithmetic on s390x.
//!
//! # Safety
//!
//! Parsing the vDSO involves a lot of raw pointer manipulation. This
Expand Down Expand Up @@ -34,6 +38,7 @@ pub(super) struct Vdso {
// Symbol table
symtab: *const Elf_Sym,
symstrings: *const u8,
gnu_hash: *const u32,
bucket: *const ElfHashEntry,
chain: *const ElfHashEntry,
nbucket: ElfHashEntry,
Expand All @@ -60,6 +65,16 @@ fn elf_hash(name: &CStr) -> u32 {
h
}

fn gnu_hash(name: &CStr) -> u32 {
let mut h: u32 = 5381;
for s in name.to_bytes() {
h = h
.wrapping_add(h.wrapping_mul(32))
.wrapping_add(u32::from(*s));
}
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
Expand All @@ -80,6 +95,7 @@ fn init_from_sysinfo_ehdr() -> Option<Vdso> {
pv_offset: 0,
symtab: null(),
symstrings: null(),
gnu_hash: null(),
bucket: null(),
chain: null(),
nbucket: 0,
Expand Down Expand Up @@ -159,6 +175,11 @@ fn init_from_sysinfo_ehdr() -> Option<Vdso> {
)?
.as_ptr();
}
DT_GNU_HASH => {
vdso.gnu_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 _)?
Expand All @@ -183,7 +204,10 @@ fn init_from_sysinfo_ehdr() -> Option<Vdso> {
// `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() {
if vdso.symstrings.is_null()
|| vdso.symtab.is_null()
|| (hash.is_null() && vdso.gnu_hash.is_null())
{
return None; // Failed
}

Expand All @@ -192,10 +216,21 @@ fn init_from_sysinfo_ehdr() -> Option<Vdso> {
}

// 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);
if !vdso.gnu_hash.is_null() {
vdso.nbucket = ElfHashEntry::from(*vdso.gnu_hash);
// The bucket array is located after the header (4 uint32) and the bloom
// filter (size_t array of gnu_hash[2] elements).
vdso.bucket = vdso
.gnu_hash
.add(4)
.add(size_of::<c::size_t>() / 4 * *vdso.gnu_hash.add(2) as usize)
.cast();
} else {
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)
Expand Down Expand Up @@ -261,49 +296,110 @@ impl Vdso {
&& (name == CStr::from_ptr(self.symstrings.add(aux.vda_name as usize).cast()))
}

/// Check to see if the symbol is the one we're looking for.
///
/// # Safety
///
/// The raw pointers inside `self` must be valid.
unsafe fn check_sym(
&self,
sym: &Elf_Sym,
i: ElfHashEntry,
name: &CStr,
version: &CStr,
ver_hash: u32,
) -> bool {
// Check for a defined global or weak function w/ right name.
//
// 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 {
return false;
}
if ELF_ST_BIND(sym.st_info) != STB_GLOBAL && ELF_ST_BIND(sym.st_info) != STB_WEAK {
return false;
}
if name != CStr::from_ptr(self.symstrings.add(sym.st_name as usize).cast()) {
return false;
}

// Check symbol version.
if !self.versym.is_null()
&& !self.match_version(*self.versym.add(i as usize), version, ver_hash)
{
return false;
}

true
}

/// 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((ElfHashEntry::from(name_hash) % self.nbucket) as usize);

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.
//
// 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
&& 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;
if !self.gnu_hash.is_null() {
let mut h1: u32 = gnu_hash(name);

// Changes to fix the pointer arithmetic on s390x: cast
// `self.bucket` to `*const u32` here, because even though
// s390x's `ElfHashEntry` is 64-bit for `DT_HASH` tables,
// it uses 32-bit entries for `DT_GNU_HASH` tables.
let mut i = *self
.bucket
.cast::<u32>()
.add((ElfHashEntry::from(h1) % self.nbucket) as usize);
if i == 0 {
return null_mut();
}
h1 |= 1;
// Changes to fix the pointer arithmetic on s390x: As above,
// cast `self.bucket` to `*const u32`.
let mut hashval = self
.bucket
.cast::<u32>()
.add(self.nbucket as usize)
.add((i - *self.gnu_hash.add(1)) as usize);
loop {
let sym: &Elf_Sym = &*self.symtab.add(i as usize);
let h2 = *hashval;
hashval = hashval.add(1);
if h1 == (h2 | 1)
&& self.check_sym(sym, ElfHashEntry::from(i), name, version, ver_hash)
{
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;
}
if (h2 & 1) != 0 {
break;
}
i += 1;
}
} else {
let mut i = *self
.bucket
.add((ElfHashEntry::from(elf_hash(name)) % self.nbucket) as usize);
while i != 0 {
let sym: &Elf_Sym = &*self.symtab.add(i as usize);
if sym.st_shndx != SHN_UNDEF && self.check_sym(sym, i, name, version, ver_hash)
{
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;
}
i = *self.chain.add(i as usize);
}

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;
}
}

Expand All @@ -324,32 +420,103 @@ impl Vdso {
}
}

// Disable on MIPS since QEMU on MIPS doesn't provide a vDSO.
#[cfg(linux_raw)]
#[test]
#[ignore] // Until rustix is updated to the new vDSO format.
#[cfg_attr(any(target_arch = "mips", target_arch = "mips64"), ignore)]
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());
{
#[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());
}

{
#[cfg(target_arch = "x86_64")]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_getres"));
#[cfg(target_arch = "arm")]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_getres"));
#[cfg(target_arch = "aarch64")]
let ptr = vdso.sym(cstr!("LINUX_2.6.39"), cstr!("__kernel_clock_getres"));
#[cfg(target_arch = "x86")]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_getres"));
#[cfg(target_arch = "riscv64")]
let ptr = vdso.sym(cstr!("LINUX_4.15"), cstr!("__vdso_clock_getres"));
#[cfg(target_arch = "powerpc64")]
let ptr = vdso.sym(cstr!("LINUX_2.6.15"), cstr!("__kernel_clock_getres"));
#[cfg(target_arch = "s390x")]
let ptr = vdso.sym(cstr!("LINUX_2.6.29"), cstr!("__kernel_clock_getres"));
#[cfg(any(target_arch = "mips", target_arch = "mips32r6"))]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_getres"));
#[cfg(any(target_arch = "mips64", target_arch = "mips64r6"))]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_clock_getres"));

assert!(!ptr.is_null());
}

{
#[cfg(target_arch = "x86_64")]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_gettimeofday"));
#[cfg(target_arch = "arm")]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_gettimeofday"));
#[cfg(target_arch = "aarch64")]
let ptr = vdso.sym(cstr!("LINUX_2.6.39"), cstr!("__kernel_gettimeofday"));
#[cfg(target_arch = "x86")]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_gettimeofday"));
#[cfg(target_arch = "riscv64")]
let ptr = vdso.sym(cstr!("LINUX_4.15"), cstr!("__vdso_gettimeofday"));
#[cfg(target_arch = "powerpc64")]
let ptr = vdso.sym(cstr!("LINUX_2.6.15"), cstr!("__kernel_gettimeofday"));
#[cfg(target_arch = "s390x")]
let ptr = vdso.sym(cstr!("LINUX_2.6.29"), cstr!("__kernel_gettimeofday"));
#[cfg(any(target_arch = "mips", target_arch = "mips32r6"))]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_gettimeofday"));
#[cfg(any(target_arch = "mips64", target_arch = "mips64r6"))]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_gettimeofday"));

assert!(!ptr.is_null());
}

#[cfg(any(
target_arch = "x86_64",
target_arch = "x86",
target_arch = "riscv64",
target_arch = "powerpc64",
target_arch = "s390x",
))]
{
#[cfg(target_arch = "x86_64")]
let ptr = vdso.sym(cstr!("LINUX_2.6"), cstr!("__vdso_getcpu"));
#[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!("__vdso_getcpu"));
#[cfg(target_arch = "powerpc64")]
let ptr = vdso.sym(cstr!("LINUX_2.6.15"), cstr!("__kernel_getcpu"));
#[cfg(target_arch = "s390x")]
let ptr = vdso.sym(cstr!("LINUX_2.6.29"), cstr!("__kernel_getcpu"));

assert!(!ptr.is_null());
}
}
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