elf_loader 0.15.0

//! Parsing `.dynamic` section
use crate::{
    ParseDynamicError, Result,
    arch::NativeArch,
    elf::{
        ElfDynRaw, ElfDynamicTag, ElfLayout, ElfRel, ElfRelType, ElfRela, ElfRelr, NativeElfLayout,
    },
    relocation::RelocationArch,
    segment::ElfSegments,
};
use alloc::vec::Vec;
use core::fmt::Debug;
use core::marker::PhantomData;
use core::{num::NonZeroUsize, ptr::NonNull};
use elf::abi::*;

/// ELF dynamic section entry.
#[derive(Debug)]
#[repr(transparent)]
pub struct ElfDyn<L: ElfLayout = NativeElfLayout> {
    dyn_: L::Dyn,
}

impl<L: ElfLayout> ElfDyn<L> {
    /// Creates an owned ELF dynamic entry from a tag and payload value.
    #[inline]
    pub fn new(tag: ElfDynamicTag, value: usize) -> Self {
        let mut dyn_: L::Dyn = unsafe { core::mem::zeroed() };
        dyn_.set_d_tag(tag.raw());
        dyn_.set_d_un(value);
        Self { dyn_ }
    }

    /// Returns the parsed ELF dynamic tag of this entry.
    #[inline]
    pub fn tag(&self) -> ElfDynamicTag {
        ElfDynamicTag::new(self.dyn_.d_tag())
    }

    /// Returns the dynamic value or pointer payload.
    #[inline]
    pub fn value(&self) -> usize {
        self.dyn_.d_un()
    }

    /// Sets the dynamic tag (`d_tag`).
    #[inline]
    pub fn set_tag(&mut self, tag: ElfDynamicTag) {
        self.dyn_.set_d_tag(tag.raw());
    }

    /// Sets the dynamic payload value (`d_un`).
    #[inline]
    pub fn set_value(&mut self, value: usize) {
        self.dyn_.set_d_un(value);
    }
}

/// Raw dynamic-section fields decoded from the DT entries.
#[derive(Debug, Default)]
pub(crate) struct ParsedDynamic {
    pub(crate) symtab_off: usize,
    pub(crate) strtab_off: usize,
    pub(crate) strtab_size: Option<NonZeroUsize>,
    pub(crate) elf_hash_off: Option<usize>,
    pub(crate) gnu_hash_off: Option<usize>,
    pub(crate) got_off: Option<NonZeroUsize>,
    pub(crate) pltrel_size: Option<NonZeroUsize>,
    pub(crate) pltrel_off: Option<NonZeroUsize>,
    pub(crate) rel_off: Option<NonZeroUsize>,
    pub(crate) rel_size: Option<NonZeroUsize>,
    pub(crate) rel_count: Option<NonZeroUsize>,
    pub(crate) relr_off: Option<NonZeroUsize>,
    pub(crate) relr_size: Option<NonZeroUsize>,
    pub(crate) init_off: Option<NonZeroUsize>,
    pub(crate) fini_off: Option<NonZeroUsize>,
    pub(crate) init_array_off: Option<NonZeroUsize>,
    pub(crate) init_array_size: Option<NonZeroUsize>,
    pub(crate) fini_array_off: Option<NonZeroUsize>,
    pub(crate) fini_array_size: Option<NonZeroUsize>,
    pub(crate) version_ids_off: Option<NonZeroUsize>,
    pub(crate) verneed_off: Option<NonZeroUsize>,
    pub(crate) verneed_num: Option<NonZeroUsize>,
    pub(crate) verdef_off: Option<NonZeroUsize>,
    pub(crate) verdef_num: Option<NonZeroUsize>,
    pub(crate) soname_off: Option<NonZeroUsize>,
    pub(crate) rpath_off: Option<NonZeroUsize>,
    pub(crate) runpath_off: Option<NonZeroUsize>,
    pub(crate) bind_now: bool,
    pub(crate) flags: usize,
    pub(crate) flags_1: usize,
    pub(crate) is_rela: Option<bool>,
    pub(crate) needed_libs: Vec<NonZeroUsize>,
}

impl ParsedDynamic {
    #[inline]
    fn apply(&mut self, tag: ElfDynamicTag, value: usize) -> bool {
        match tag {
            ElfDynamicTag::FLAGS => self.flags = value,
            ElfDynamicTag::FLAGS_1 => self.flags_1 = value,
            ElfDynamicTag::PLTGOT => self.got_off = NonZeroUsize::new(value),
            ElfDynamicTag::NEEDED => {
                if let Some(val) = NonZeroUsize::new(value) {
                    self.needed_libs.push(val);
                }
            }
            ElfDynamicTag::HASH => self.elf_hash_off = Some(value),
            ElfDynamicTag::GNU_HASH => self.gnu_hash_off = Some(value),
            ElfDynamicTag::BIND_NOW => self.bind_now = true,
            ElfDynamicTag::SONAME => self.soname_off = NonZeroUsize::new(value),
            ElfDynamicTag::SYMTAB => self.symtab_off = value,
            ElfDynamicTag::STRTAB => self.strtab_off = value,
            ElfDynamicTag::PLTRELSZ => self.pltrel_size = NonZeroUsize::new(value),
            ElfDynamicTag::PLTREL => {
                self.is_rela = Some(ElfDynamicTag::new(value as i64) == ElfDynamicTag::RELA);
            }
            ElfDynamicTag::JMPREL => self.pltrel_off = NonZeroUsize::new(value),
            ElfDynamicTag::RELR => self.relr_off = NonZeroUsize::new(value),
            ElfDynamicTag::RELA | ElfDynamicTag::REL => {
                self.is_rela = Some(tag == ElfDynamicTag::RELA);
                self.rel_off = NonZeroUsize::new(value)
            }
            ElfDynamicTag::RELASZ | ElfDynamicTag::RELSZ => {
                self.rel_size = NonZeroUsize::new(value)
            }
            ElfDynamicTag::RELRSZ => self.relr_size = NonZeroUsize::new(value),
            ElfDynamicTag::RELACOUNT | ElfDynamicTag::RELCOUNT => {
                self.rel_count = NonZeroUsize::new(value)
            }
            ElfDynamicTag::INIT => self.init_off = NonZeroUsize::new(value),
            ElfDynamicTag::FINI => self.fini_off = NonZeroUsize::new(value),
            ElfDynamicTag::INIT_ARRAY => self.init_array_off = NonZeroUsize::new(value),
            ElfDynamicTag::INIT_ARRAYSZ => self.init_array_size = NonZeroUsize::new(value),
            ElfDynamicTag::FINI_ARRAY => self.fini_array_off = NonZeroUsize::new(value),
            ElfDynamicTag::FINI_ARRAYSZ => self.fini_array_size = NonZeroUsize::new(value),
            ElfDynamicTag::VERSYM => self.version_ids_off = NonZeroUsize::new(value),
            ElfDynamicTag::VERNEED => self.verneed_off = NonZeroUsize::new(value),
            ElfDynamicTag::VERNEEDNUM => self.verneed_num = NonZeroUsize::new(value),
            ElfDynamicTag::VERDEF => self.verdef_off = NonZeroUsize::new(value),
            ElfDynamicTag::VERDEFNUM => self.verdef_num = NonZeroUsize::new(value),
            ElfDynamicTag::RPATH => self.rpath_off = NonZeroUsize::new(value),
            ElfDynamicTag::RUNPATH => self.runpath_off = NonZeroUsize::new(value),
            ElfDynamicTag::STRSZ => self.strtab_size = NonZeroUsize::new(value),
            ElfDynamicTag::NULL => return true,
            _ => {}
        }

        false
    }
}

/// Parses a stream of dynamic-section entries into raw offsets and flags.
#[inline]
pub(crate) fn parse_dynamic_entries<I>(entries: I) -> ParsedDynamic
where
    I: IntoIterator<Item = (ElfDynamicTag, usize)>,
{
    let mut parsed = ParsedDynamic::default();
    for (tag, value) in entries {
        if parsed.apply(tag, value) {
            break;
        }
    }
    parsed
}

struct DynamicPtrIter<L: ElfLayout = NativeElfLayout> {
    cur: *const ElfDyn<L>,
    done: bool,
    _marker: PhantomData<ElfDyn<L>>,
}

impl<L: ElfLayout> DynamicPtrIter<L> {
    #[inline]
    fn new(cur: *const ElfDyn<L>) -> Self {
        Self {
            cur,
            done: false,
            _marker: PhantomData,
        }
    }
}

impl<L: ElfLayout> Iterator for DynamicPtrIter<L> {
    type Item = (ElfDynamicTag, usize);

    fn next(&mut self) -> Option<Self::Item> {
        if self.done {
            return None;
        }

        unsafe {
            let dynamic = &*self.cur;
            let tag = dynamic.tag();
            let value = dynamic.value();
            self.cur = self.cur.add(1);
            if tag == ElfDynamicTag::NULL {
                self.done = true;
            }
            Some((tag, value))
        }
    }
}

impl<Arch> ElfDynamic<Arch>
where
    Arch: RelocationArch,
{
    /// Parse the dynamic section of an ELF file
    pub fn new(dynamic_ptr: *const ElfDyn<Arch::Layout>, segments: &ElfSegments) -> Result<Self> {
        let parsed = parse_dynamic_entries(DynamicPtrIter::new(dynamic_ptr));
        let base = segments.base();

        // Verify relocation type consistency
        if let Some(is_rela) = parsed.is_rela {
            assert!(
                is_rela && size_of::<Arch::Relocation>() == size_of::<ElfRela<Arch::Layout>>()
                    || !is_rela
                        && size_of::<Arch::Relocation>() == size_of::<ElfRel<Arch::Layout>>()
            );
        }

        let add_base = |offset: usize| -> Result<usize> {
            base.checked_add(offset)
                .ok_or(ParseDynamicError::AddressOverflow.into())
        };
        let add_base_nonzero = |offset: NonZeroUsize| -> Result<NonZeroUsize> {
            NonZeroUsize::new(add_base(offset.get())?)
                .ok_or_else(|| ParseDynamicError::AddressOverflow.into())
        };

        // Determine which hash table to use (prefer GNU hash)
        let hash_off = if let Some(off) = parsed.gnu_hash_off {
            ElfDynamicHashTab::Gnu(add_base(off)?)
        } else if let Some(off) = parsed.elf_hash_off {
            ElfDynamicHashTab::Elf(add_base(off)?)
        } else {
            return Err(ParseDynamicError::MissingRequiredTag {
                tag: "DT_GNU_HASH or DT_HASH",
            }
            .into());
        };

        // Extract relocation tables
        let pltrel = parsed.pltrel_off.map(|pltrel_off| {
            segments.get_slice(
                pltrel_off.get(),
                parsed.pltrel_size.map(|s| s.get()).unwrap_or(0),
            )
        });
        let dynrel = parsed.rel_off.map(|rel_off| {
            segments.get_slice(rel_off.get(), parsed.rel_size.map(|s| s.get()).unwrap_or(0))
        });
        let relr = parsed.relr_off.map(|relr_off| {
            segments.get_slice(
                relr_off.get(),
                parsed.relr_size.map(|s| s.get()).unwrap_or(0),
            )
        });

        // Extract initialization and finalization functions
        let init_fn = parsed
            .init_off
            .map(|val| unsafe { core::mem::transmute(segments.get_ptr::<fn()>(val.get())) });
        let init_array_fn = parsed.init_array_off.map(|init_array_off| {
            segments.get_slice(
                init_array_off.get(),
                parsed.init_array_size.map(|s| s.get()).unwrap_or(0),
            )
        });
        let fini_fn = parsed.fini_off.map(|fini_off| unsafe {
            core::mem::transmute(segments.get_ptr::<fn()>(fini_off.get()))
        });
        let fini_array_fn = parsed.fini_array_off.map(|fini_array_off| {
            segments.get_slice(
                fini_array_off.get(),
                parsed.fini_array_size.map(|s| s.get()).unwrap_or(0),
            )
        });

        // Extract versioning information
        let verneed = parsed
            .verneed_off
            .map(|verneed_off| -> Result<_> {
                Ok((
                    add_base_nonzero(verneed_off)?,
                    parsed
                        .verneed_num
                        .ok_or(ParseDynamicError::MissingRequiredTag {
                            tag: "DT_VERNEEDNUM",
                        })?,
                ))
            })
            .transpose()?;
        let verdef = parsed
            .verdef_off
            .map(|verdef_off| -> Result<_> {
                Ok((
                    add_base_nonzero(verdef_off)?,
                    parsed
                        .verdef_num
                        .ok_or(ParseDynamicError::MissingRequiredTag {
                            tag: "DT_VERDEFNUM",
                        })?,
                ))
            })
            .transpose()?;
        let version_idx = parsed.version_ids_off.map(add_base_nonzero).transpose()?;

        Ok(ElfDynamic {
            dyn_ptr: dynamic_ptr,
            hashtab: hash_off,
            symtab: add_base(parsed.symtab_off)?,
            strtab: add_base(parsed.strtab_off)?,
            // Check if binding should be done immediately
            bind_now: parsed.bind_now
                || parsed.flags & DF_BIND_NOW as usize != 0
                || parsed.flags_1 & DF_1_NOW as usize != 0,
            static_tls: parsed.flags & DF_STATIC_TLS as usize != 0,
            got_plt: parsed
                .got_off
                .map(|off| add_base(off.get()))
                .transpose()?
                .map(|addr| unsafe { NonNull::new_unchecked(addr as *mut usize) }),
            needed_libs: parsed.needed_libs,
            pltrel,
            dynrel,
            relr,
            init_fn,
            init_array_fn,
            fini_fn,
            fini_array_fn,
            rel_count: parsed.rel_count,
            soname_off: parsed.soname_off,
            rpath_off: parsed.rpath_off,
            runpath_off: parsed.runpath_off,
            version_idx,
            verneed,
            verdef,
        })
    }
}

/// Hash table type used for symbol lookup
pub enum ElfDynamicHashTab {
    /// GNU-style hash table (DT_GNU_HASH)
    Gnu(usize),
    /// Traditional ELF hash table (DT_HASH)
    Elf(usize),
}

#[allow(unused)]
/// Information from the ELF dynamic section.
pub(crate) struct ElfDynamic<Arch: RelocationArch = NativeArch> {
    /// Pointer to the dynamic section.
    pub dyn_ptr: *const ElfDyn<Arch::Layout>,
    /// Hash table information.
    pub hashtab: ElfDynamicHashTab,
    /// Symbol table address.
    pub symtab: usize,
    /// String table address.
    pub strtab: usize,
    /// Whether to bind symbols immediately.
    pub bind_now: bool,
    /// Whether the object uses static thread-local storage.
    pub static_tls: bool,
    /// Global Offset Table address.
    pub got_plt: Option<NonNull<usize>>,
    /// Initialization function.
    pub init_fn: Option<fn()>,
    /// Initialization function array.
    pub init_array_fn: Option<&'static [fn()]>,
    /// Finalization function.
    pub fini_fn: Option<fn()>,
    /// Finalization function array.
    pub fini_array_fn: Option<&'static [fn()]>,
    /// PLT relocation entries.
    pub pltrel: Option<&'static [ElfRelType<Arch>]>,
    /// Dynamic relocation entries.
    pub dynrel: Option<&'static [ElfRelType<Arch>]>,
    /// RELR relocation entries.
    pub relr: Option<&'static [ElfRelr<Arch::Layout>]>,
    /// Count of relative relocations.
    pub rel_count: Option<NonZeroUsize>,
    /// Required libraries.
    pub needed_libs: Vec<NonZeroUsize>,
    /// Symbol version index.
    pub version_idx: Option<NonZeroUsize>,
    /// Version needed information.
    pub verneed: Option<(NonZeroUsize, NonZeroUsize)>,
    /// Version definition information.
    pub verdef: Option<(NonZeroUsize, NonZeroUsize)>,
    /// Shared-object name.
    pub soname_off: Option<NonZeroUsize>,
    /// Runtime library search path.
    pub rpath_off: Option<NonZeroUsize>,
    /// Runtime library search path (overrides RPATH).
    pub runpath_off: Option<NonZeroUsize>,
}

impl<Arch: RelocationArch> Debug for ElfDynamic<Arch> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.debug_struct("ElfDynamic")
            .field("dyn_ptr", &self.dyn_ptr)
            .field("symtab", &format_args!("0x{:x}", self.symtab))
            .field("strtab", &format_args!("0x{:x}", self.strtab))
            .field("bind_now", &self.bind_now)
            .field("static_tls", &self.static_tls)
            .field("got_plt", &self.got_plt)
            .field("needed_libs_count", &self.needed_libs.len())
            .field("pltrel_count", &self.pltrel.map(|r| r.len()).unwrap_or(0))
            .field("dynrel_count", &self.dynrel.map(|r| r.len()).unwrap_or(0))
            .field("relr_count", &self.relr.map(|r| r.len()).unwrap_or(0))
            .finish()
    }
}

#[cfg(test)]
mod tests {
    use super::{ElfDyn, ElfDynamicTag, parse_dynamic_entries};
    use core::num::NonZeroUsize;

    #[test]
    fn owned_dyn_round_trips_and_mutates() {
        let mut dyn_: ElfDyn = ElfDyn::new(ElfDynamicTag::STRTAB, 0x1234);
        assert_eq!(dyn_.tag(), ElfDynamicTag::STRTAB);
        assert_eq!(dyn_.value(), 0x1234);

        dyn_.set_tag(ElfDynamicTag::NULL);
        dyn_.set_value(0x5678);
        assert_eq!(dyn_.tag(), ElfDynamicTag::NULL);
        assert_eq!(dyn_.value(), 0x5678);
    }

    #[test]
    fn parses_metadata_only_dynamic_tags() {
        let parsed = parse_dynamic_entries([
            (ElfDynamicTag::SONAME, 0x24),
            (ElfDynamicTag::BIND_NOW, 0),
            (ElfDynamicTag::NULL, 0),
        ]);

        assert_eq!(parsed.soname_off, NonZeroUsize::new(0x24));
        assert!(parsed.bind_now);
    }
}