From b72b4ab9e9a859b4ab8ce08728da297efa89bce8 Mon Sep 17 00:00:00 2001 From: Astro Date: Sat, 25 Apr 2020 21:17:11 +0200 Subject: [PATCH] libdyld: add resolve_rel() --- libdyld/src/lib.rs | 90 +++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 89 insertions(+), 1 deletion(-) diff --git a/libdyld/src/lib.rs b/libdyld/src/lib.rs index c6aa5f0..156f8ed 100644 --- a/libdyld/src/lib.rs +++ b/libdyld/src/lib.rs @@ -158,6 +158,16 @@ impl<'a> Library<'a> { Ok(unsafe { *ptr = value }) } + + fn update_rel(&self, rel: &Elf32_Rel, value: Elf32_Word) -> Result<(), Error<'a>> { + if rel.r_offset as usize + mem::size_of::() > self.image_sz { + return Err("relocation out of image bounds")? + } + + let ptr = (self.image_off + rel.r_offset) as *mut Elf32_Addr; + Ok(unsafe { *ptr = value }) + } + // This is unsafe because it mutates global data (the PLT). pub unsafe fn rebind(&self, name: &[u8], addr: Elf32_Word) -> Result<(), Error<'a>> { for rela in self.pltrel.iter() { @@ -250,6 +260,74 @@ impl<'a> Library<'a> { self.update_rela(rela, value) } + fn resolve_rel(&self, rel: &Elf32_Rel, resolve: &dyn Fn(&[u8]) -> Option) + -> Result<(), Error<'a>> { + #[derive(Debug)] + enum RelType { + None, + Relative, + Lookup, + }; + let rel_type = match ELF32_R_TYPE(rel.r_info) { + R_OR1K_NONE if self.arch == Arch::OpenRisc => + RelType::None, + R_ARM_NONE if self.arch == Arch::Arm => + RelType::None, + + R_OR1K_RELATIVE if self.arch == Arch::OpenRisc => + RelType::Relative, + R_ARM_RELATIVE if self.arch == Arch::Arm => + RelType::Relative, + + R_OR1K_32 | R_OR1K_GLOB_DAT | R_OR1K_JMP_SLOT + if self.arch == Arch::OpenRisc => RelType::Lookup, + R_ARM_GLOB_DAT | R_ARM_JUMP_SLOT + if self.arch == Arch::Arm => RelType::Lookup, + + _ => + return Err("unsupported relocation type")?, + }; + let value; + match rel_type { + RelType::None => + return Ok(()), + + RelType::Relative => { + let addend = unsafe { + *((self.image_off + rel.r_offset) as *const Elf32_Addr) + }; + value = self.image_off + addend as Elf32_Word; + }, + + RelType::Lookup => { + let sym; + if ELF32_R_SYM(rel.r_info) == 0 { + return Err("relocation requires an associated symbol")?; + } + sym = self.symtab.get(ELF32_R_SYM(rel.r_info) as usize) + .ok_or("symbol out of bounds of symbol table")?; + let sym_name = self.name_starting_at(sym.st_name as usize)?; + + // First, try to resolve against itself. + match self.lookup(sym_name) { + Some(addr) => value = addr, + None => { + // Second, call the user-provided function. + match resolve(sym_name) { + Some(addr) => value = addr, + None => { + // We couldn't find it anywhere. + return Err(Error::Lookup(sym_name)) + } + } + } + } + } + } + + self.update_rel(rel, value) + } + pub fn load(data: &[u8], image: &'a mut [u8], resolve: &dyn Fn(&[u8]) -> Option) -> Result, Error<'a>> { #![allow(unused_assignments)] @@ -296,10 +374,12 @@ impl<'a> Library<'a> { let (mut strtab_off, mut strtab_sz) = (0, 0); let (mut symtab_off, mut symtab_sz) = (0, 0); + let (mut rel_off, mut rel_sz) = (0, 0); let (mut rela_off, mut rela_sz) = (0, 0); let (mut pltrel_off, mut pltrel_sz) = (0, 0); let (mut hash_off, mut hash_sz) = (0, 0); let mut sym_ent = 0; + let mut rel_ent = 0; let mut rela_ent = 0; let mut nbucket = 0; let mut nchain = 0; @@ -313,11 +393,13 @@ impl<'a> Library<'a> { let val = unsafe { dyn.d_un.d_val } as usize; match dyn.d_tag { DT_NULL => break, - DT_REL => return Err("relocations with implicit addend are not supported")?, DT_STRTAB => strtab_off = val, DT_STRSZ => strtab_sz = val, DT_SYMTAB => symtab_off = val, DT_SYMENT => sym_ent = val, + DT_REL => rel_off = val, + DT_RELSZ => rel_sz = val / mem::size_of::(), + DT_RELENT => rel_ent = val, DT_RELA => rela_off = val, DT_RELASZ => rela_sz = val / mem::size_of::(), DT_RELAENT => rela_ent = val, @@ -338,6 +420,9 @@ impl<'a> Library<'a> { if sym_ent != mem::size_of::() { return Err("incorrect symbol entry size")? } + if rel_ent != 0 && rel_ent != mem::size_of::() { + return Err("incorrect relocation entry size")? + } if rela_ent != 0 && rela_ent != mem::size_of::() { return Err("incorrect relocation entry size")? } @@ -353,6 +438,8 @@ impl<'a> Library<'a> { .map_err(|()| "cannot read string table")?; let symtab = get_ref_slice::(image, symtab_off, symtab_sz) .map_err(|()| "cannot read symbol table")?; + let rel = get_ref_slice::(image, rel_off, rel_sz) + .map_err(|()| "cannot read rel entries")?; let rela = get_ref_slice::(image, rela_off, rela_sz) .map_err(|()| "cannot read rela entries")?; let pltrel = get_ref_slice::(image, pltrel_off, pltrel_sz) @@ -382,6 +469,7 @@ impl<'a> Library<'a> { mem::drop(image); for r in rela { library.resolve_rela(r, resolve)? } + for r in rel { library.resolve_rel(r, resolve)? } for r in pltrel { library.resolve_rela(r, resolve)? } Ok(library)