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Add support for ELF thread-local storage #419

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Add support for ELF thread-local storage #419

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24 changes: 18 additions & 6 deletions doc/FORTANIX-SGX-ELF.md
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Original file line number Diff line number Diff line change
Expand Up @@ -32,19 +32,25 @@ This section describes the requirements on the SGX thread control structure
### TCS

- `NSSA` should be set to 1.
- `OGSBASGX` should point to a thread-specific memory region (e.g. TLS) of at
least 112 bytes.
- `OFSBASGX` should point to a thread-specific memory region of at least 120 bytes
with 8-byte alignment.
- For backwards-compatibility reasons, `OGSBASGX` should be set to `OFSBASGX + 8`.

### TLS

The memory region pointed to by `OGSBASGX` should be initialized as follows:
The memory region pointed to by `OFSBASGX` should be initialized as follows:

- Offset `0x0`: Top-of-Stack offset from image base.
- Offset `0x8`: `1` if this is an executable and this is a secondary TCS, `0`
- Offset `0x0`: Value of `OSFSBASX`.
- Offset `0x8`: Top-of-Stack offset from image base.
- Offset `0x10`: `1` if this is an executable and this is a secondary TCS, `0`
otherwise.
- Offsets `0x10`, `0x18`, `0x20`: `0`
- Offsets `0x18`, `0x20`, `0x28`: `0`
- Other offsets: uninitialized.

If the program uses ELF TLS segments (with the local exec model), `OSFSBASGX`
should point to the end of a memory region capable of holding the TLS data and
be suitably aligned for that purpose.

## Globals

This section describes the requirements for various global constants in the SGX
Expand All @@ -70,3 +76,9 @@ binary.
of the ELF section named '.eh_frame'.
- `EH_FRM_LEN`. Size 8 bytes. The size in bytes of the ELF section named
'.eh_frame'.
- `TLS_INIT_BASE`. Size 8 bytes. The base address of the TLS initialization image,
little-endian.
- `TLS_INIT_SIZE`. Size 8 bytes. The size of the TLS initialization image,
little-endian.
- `TLS_OFFSET`. Size 8 bytes. The TLS offset of the main module (see the [ELF-TLS
specification](https://uclibc.org/docs/tls.pdf) for more information).
151 changes: 127 additions & 24 deletions intel-sgx/fortanix-sgx-tools/src/bin/ftxsgx-elf2sgxs.rs
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Expand Up @@ -14,7 +14,7 @@ extern crate failure;

use std::borrow::Borrow;
use std::fs::File;
use std::io::{repeat, Error as IoError, Read};
use std::io::{self, repeat, Error as IoError, Read};
use std::mem::replace;
use std::num::ParseIntError;
use std::path::{Path, PathBuf};
Expand All @@ -35,6 +35,9 @@ use sgxs_crate::util::{size_fit_natural, size_fit_page};
use clap::ArgMatches;
use std::convert::TryInto;

const THREAD_GUARD_SIZE: u64 = 0x10000;
const TCB_SIZE: u64 = 120;

#[allow(non_snake_case)]
struct Symbols<'a> {
sgx_entry: &'a DynSymEntry,
Expand All @@ -53,7 +56,11 @@ struct Symbols<'a> {
EH_FRM_LEN: Option<&'a DynSymEntry>,
EH_FRM_HDR_OFFSET: Option<&'a DynSymEntry>,
EH_FRM_HDR_LEN: Option<&'a DynSymEntry>,
TLS_INIT_BASE: Option<&'a DynSymEntry>,
TLS_INIT_SIZE: Option<&'a DynSymEntry>,
TLS_OFFSET: Option<&'a DynSymEntry>,
}

struct SectionRange {
offset: u64,
size: u64,
Expand All @@ -64,6 +71,19 @@ struct Dynamic<'a> {
relacount: &'a DynEntry<u64>,
}

struct Tls {
init_base: u64,
init_size: u64,
/// The module offset from the thread pointer (see the ELF-TLS specification
/// for more details)
module_offset: u64,
/// The size of the TLS area for one thread (page-aligned)
size: u64,
/// The offset of the thread pointer (hence also the TCB) from the start of
/// the TLS area
tp_offset: u64,
}

struct Splice {
address: u64,
value: Vec<u8>,
Expand Down Expand Up @@ -119,6 +139,7 @@ pub struct LayoutInfo<'a> {
ehfrm: SectionRange,
ehfrm_hdr: SectionRange,
text: SectionRange,
tls: Tls,
}

macro_rules! read_syms {
Expand Down Expand Up @@ -233,10 +254,9 @@ impl<'a> LayoutInfo<'a> {
//
// Variables have been renamed due to missing 'toolchain' version checks. Rename will cause compile-time failure if using old tool with new toolchain assembly code.
let syms = read_syms!(mandatory: sgx_entry, HEAP_BASE, HEAP_SIZE, RELA, RELACOUNT, ENCLAVE_SIZE, CFGDATA_BASE, DEBUG, TEXT_BASE, TEXT_SIZE
optional: EH_FRM_HDR_BASE, EH_FRM_HDR_SIZE, EH_FRM_OFFSET, EH_FRM_LEN, EH_FRM_HDR_OFFSET, EH_FRM_HDR_LEN
optional: EH_FRM_HDR_BASE, EH_FRM_HDR_SIZE, EH_FRM_OFFSET, EH_FRM_LEN, EH_FRM_HDR_OFFSET, EH_FRM_HDR_LEN, TLS_INIT_BASE, TLS_INIT_SIZE, TLS_OFFSET
in syms : elf);


check_size!(syms.HEAP_BASE == 8);
check_size!(syms.HEAP_SIZE == 8);
check_size!(syms.RELA == 8);
Expand Down Expand Up @@ -264,7 +284,17 @@ impl<'a> LayoutInfo<'a> {
} else {
bail!("Missing EH Frame header symbols, application must either have (EH_FRM_HDR_BASE/EH_FRM_HDR_SIZE) or (EH_FRM_OFFSET, EH_FRM_LEN, EH_FRM_HDR_OFFSET, EH_FRM_HDR_LEN");
}


match (syms.TLS_INIT_BASE, syms.TLS_INIT_SIZE, syms.TLS_OFFSET) {
(Some(TLS_INIT_BASE), Some(TLS_INIT_SIZE), Some(TLS_OFFSET)) => {
check_size!(TLS_INIT_BASE == 8);
check_size!(TLS_INIT_SIZE == 8);
check_size!(TLS_OFFSET == 8);
}
(None, None, None) => {}
_ => bail!("Missing symbols, applications must either have all or none of TLS_INIT_BASE, TLS_INIT_SIZE and TLS_OFFSET"),
}

Ok(syms)
}

Expand Down Expand Up @@ -380,6 +410,56 @@ impl<'a> LayoutInfo<'a> {
Ok(())
}

fn check_tls(elf: &ElfFile<'a>) -> Result<Tls, Error> {
fn round_up(addr: u64, align: u64) -> u64 {
addr + addr.wrapping_neg() & (align - 1)
}

let mut ph = None;
for header in elf.program_iter() {
if header.get_type().map_err(err_msg)? == PhType::Tls && ph.replace(header).is_some() {
bail!("Found TLS segment twice");
}
}

if let Some(ph) = ph {
if ph.align() > 0x1000 {
bail!("Cannot guarantee more than page-alignment");
} else if !ph.align().is_power_of_two() {
bail!("Invalid TLS area alignment");
}

// The linker computes the TLS offsets assuming that
// init_base mod align == tp - module_offset mod align
// If
// init_base mod align == 0
// the following formula reduces to the formula given by the specification.
let module_offset =
round_up(ph.virtual_addr() + ph.mem_size(), ph.align()) - ph.virtual_addr();
// Compute the thread pointer offset from the start of the TLS area.
// For the assumption above to work, it needs to be properly aligned
// for the segment. Also, the thread control block needs a minimum
// alignment of 8 bytes.
let tp_offset = round_up(module_offset, u64::max(8, ph.align()));
let size = round_up(tp_offset + TCB_SIZE, 0x1000);
Ok(Tls {
init_base: ph.virtual_addr(),
init_size: ph.file_size(),
module_offset,
size,
tp_offset,
})
} else {
Ok(Tls {
init_base: 0,
init_size: 0,
module_offset: 0,
size: round_up(TCB_SIZE, 0x1000),
tp_offset: 0,
})
}
}

pub fn new(
elf: ElfFile<'a>,
ssaframesize: u32,
Expand All @@ -401,6 +481,7 @@ impl<'a> LayoutInfo<'a> {
let ehfrm = Self::check_section(&elf, ".eh_frame")?;
let ehfrm_hdr = Self::check_section(&elf, ".eh_frame_hdr")?;
let text = Self::check_section(&elf, ".text")?;
let tls = Self::check_tls(&elf)?;

Ok(LayoutInfo {
elf,
Expand All @@ -416,6 +497,7 @@ impl<'a> LayoutInfo<'a> {
ehfrm_hdr,
text,
sized,
tls,
})
}

Expand Down Expand Up @@ -465,6 +547,16 @@ impl<'a> LayoutInfo<'a> {
bail!("Missing .eh_frame header symbols, application must have symbols exported by rust x86_64_fortanix_unknown_sgx toolchain, either (EH_FRM_HDR_BASE/EH_FRM_HDR_SIZE) or (EH_FRM_OFFSET, EH_FRM_LEN, EH_FRM_HDR_OFFSET, EH_FRM_HDR_LEN");
}

if let (Some(TLS_INIT_BASE), Some(TLS_INIT_SIZE), Some(TLS_OFFSET)) = (
self.sym.TLS_INIT_BASE,
self.sym.TLS_INIT_SIZE,
self.sym.TLS_OFFSET,
) {
splices.push(Splice::for_sym_u64(TLS_INIT_BASE, self.tls.init_base));
splices.push(Splice::for_sym_u64(TLS_INIT_SIZE, self.tls.init_size));
splices.push(Splice::for_sym_u64(TLS_OFFSET, self.tls.module_offset));
}

if let Some(enclave_size) = enclave_size {
splices.push(Splice::for_sym_u64(self.sym.ENCLAVE_SIZE, enclave_size));
}
Expand All @@ -483,7 +575,7 @@ impl<'a> LayoutInfo<'a> {
for ph in self
.elf
.program_iter()
.filter(|ph| ph.get_type() == Ok(PhType::Load))
.filter(|ph| matches!(ph.get_type(), Ok(PhType::Load | PhType::Tls)))
{
let mut secinfo = SecinfoTruncated {
flags: PageType::Reg.into(),
Expand Down Expand Up @@ -563,23 +655,19 @@ impl<'a> LayoutInfo<'a> {
.elf
.program_iter()
.filter_map(|ph| {
if ph.get_type() == Ok(PhType::Load) {
Some(ph.virtual_addr() + ph.mem_size())
} else {
None
}
matches!(ph.get_type(), Ok(PhType::Load | PhType::Tls)).then(|| {
ph.virtual_addr() + ph.mem_size()
})
})
.max()
.ok_or_else(|| format_err!("No loadable segments found"))?;

let heap_addr = size_fit_page(max_addr);
let mut thread_start = heap_addr + self.heap_size;
const THREAD_GUARD_SIZE: u64 = 0x10000;
const TLS_SIZE: u64 = 0x1000;
let nssa = 1u32;
let thread_size = THREAD_GUARD_SIZE
+ self.stack_size
+ TLS_SIZE
+ self.tls.size
+ (1 + (nssa as u64) * (self.ssaframesize as u64)) * 0x1000;
let memory_size = thread_start + (self.threads as u64) * thread_size;
let enclave_size = if self.sized {
Expand Down Expand Up @@ -615,7 +703,8 @@ impl<'a> LayoutInfo<'a> {
let stack_addr = thread_start + THREAD_GUARD_SIZE;
let stack_tos = stack_addr + self.stack_size;
let tls_addr = stack_tos;
let tcs_addr = tls_addr + TLS_SIZE;
let tp = tls_addr + self.tls.tp_offset;
let tcs_addr = tls_addr + self.tls.size;

// Output stack
let secinfo = SecinfoTruncated {
Expand All @@ -628,26 +717,40 @@ impl<'a> LayoutInfo<'a> {
secinfo
)?;

// Output TLS
// Output TLS area
let secinfo = SecinfoTruncated {
flags: SecinfoFlags::R | SecinfoFlags::W | PageType::Reg.into(),
};

let reserve_pages = self.tls.tp_offset / 0x1000;
let remaining_data = self.tls.tp_offset % 0x1000;
writer.write_pages::<&[u8]>(None, reserve_pages as usize, Some(tls_addr), secinfo)?;

let secondary = match (self.library, i) {
(true, _) | (false, 0) => false,
(false, _) => true,
};
let tls = unsafe {
std::mem::transmute::<_, [u8; 32]>([stack_tos, secondary as u64, 0u64, 0u64])
let tcb = unsafe {
std::mem::transmute::<_, [u8; 40]>([tp, stack_tos, secondary as u64, 0u64, 0u64])
};
let secinfo = SecinfoTruncated {
flags: SecinfoFlags::R | SecinfoFlags::W | PageType::Reg.into(),
};
writer.write_pages(Some(&mut &tls[..]), 1, Some(tls_addr), secinfo)?;
// FIXME: Avoid writing so many zeroes.
let mut data = io::repeat(0).take(remaining_data).chain(&tcb[..]);
writer.write_pages(
Some(&mut data),
(self.tls.size / 0x1000 - reserve_pages) as usize,
Some(tls_addr + 0x1000 * reserve_pages),
secinfo,
)?;

// Output TCS, SSA
let tcs = Tcs {
ossa: tcs_addr + 0x1000,
nssa: nssa,
nssa,
oentry: self.sym.sgx_entry.value(),
ofsbasgx: tls_addr,
ogsbasgx: stack_tos,
ofsbasgx: tls_addr + self.tls.tp_offset,
// For backwards-compatibility reasons, GS needs to point to the
// second quadword in the TCB
ogsbasgx: tls_addr + self.tls.tp_offset + 8,
fslimit: 0xfff,
gslimit: 0xfff,
..Tcs::default()
Expand Down