R_AMD64_RELATIVE relocations implemented for EFI shim

1 files changed, 106 insertions, 0 deletions

diff --git a/lib/elf.c b/lib/elf.c
new file mode 100644
index 0000000..551a5a5
--- /dev/null
+++ b/lib/elf.c
@@ -0,0 +1,106 @@
+#include "elf.h"
+
+bool elf64_validate(Elf64_Ehdr *ehdr, unsigned type, unsigned machine)
+{
+    if (ehdr->e_ident[EI_MAG0] != ELFMAG0 ||
+            ehdr->e_ident[EI_MAG1] != ELFMAG1 ||
+            ehdr->e_ident[EI_MAG2] != ELFMAG2 ||
+            ehdr->e_ident[EI_MAG3] != ELFMAG3 ||
+            ehdr->e_ident[EI_CLASS] != ELFCLASS64 ||
+            ehdr->e_ident[EI_DATA] != ELFDATA2LSB ||
+            ehdr->e_ident[EI_VERSION] != EV_CURRENT ||
+            ehdr->e_machine != machine ||
+            ehdr->e_type != type)
+    {
+        return false;
+    }
+
+    return true;
+}
+
+size_t elf64_size(Elf64_Ehdr *ehdr, Elf64_Phdr *phdrs)
+{
+    size_t size = 0;
+
+    for (int i = 0; i < ehdr->e_phnum; i++)
+    {
+        if (phdrs[i].p_type != PT_LOAD)
+        {
+            continue;
+        }
+
+        if (phdrs[i].p_paddr + phdrs[i].p_memsz > size)
+        {
+            size = phdrs[i].p_paddr + phdrs[i].p_memsz;
+            if (phdrs[i].p_align > 1)
+            {
+                size = (size + phdrs[i].p_align - 1) &
+                    ~(phdrs[i].p_align - 1);
+            }
+        }
+    }
+
+    return size;
+}
+
+void elf64_reloc(Elf64_Ehdr *ehdr)
+{
+    // locate the dynamic segment
+    Elf64_Phdr *phdrs = (Elf64_Phdr *)(ehdr->e_phoff + (uintptr_t)ehdr);
+    Elf64_Dyn *dyn = NULL;
+    Elf64_Rela *rela = NULL;
+    size_t rela_size;
+    int rela_count;
+
+    for (int i = 0; i < ehdr->e_phnum; i++)
+    {
+        if (phdrs[i].p_type != PT_DYNAMIC) continue;
+
+        dyn = (Elf64_Dyn *)(phdrs[i].p_offset + (uintptr_t)ehdr);
+    }
+
+    // parse the dynamic segment
+    while (dyn->d_tag != DT_NULL)
+    {
+        switch (dyn->d_tag)
+        {
+            case DT_RELA:
+                rela = (Elf64_Rela *)(dyn->d_ptr + (uintptr_t)ehdr);
+                break;
+            case DT_RELASZ:
+                rela_size = dyn->d_val;
+                break;
+            case DT_RELAENT:
+                rela_count = rela_size / dyn->d_val;
+                break;
+            default:
+                break;
+        }
+        dyn++;
+    }
+
+    // perform the actual relocations
+
+    for (int i; i < rela_count; i++)
+    {
+        union
+        {
+            Elf_Byte word8;
+            Elf64_Half word16;
+            Elf64_Word word32;
+            Elf64_Xword word64;
+        }
+        *reloc_ptr = NULL;
+
+        switch (ELF64_R_TYPE(rela[i].r_info))
+        {
+            case R_AMD64_RELATIVE:
+                reloc_ptr = (void *)(rela[i].r_offset + (uintptr_t)ehdr);
+                reloc_ptr->word64 = (rela[i].r_addend + (uintptr_t)ehdr);
+                break;
+            default:
+                break;
+        }
+    }
+}
+