R_AMD64_RELATIVE relocations implemented for EFI shim

10 files changed, 160 insertions, 9 deletions

diff --git a/api/elf/elf64.h b/api/elf/elf64.h
index 4473d15..d975c35 100644
--- a/api/elf/elf64.h
+++ b/api/elf/elf64.h
@@ -18,6 +18,9 @@ typedef struct Elf64_Shdr Elf64_Shdr;
 typedef struct Elf64_Sym Elf64_Sym;
 typedef struct Elf64_Dyn Elf64_Dyn;
 
+typedef struct Elf64_Rel Elf64_Rel;
+typedef struct Elf64_Rela Elf64_Rela;
+
 #define EM_X86_64 62
 
 struct Elf64_Ehdr
@@ -84,3 +87,22 @@ struct Elf64_Dyn
     };
 };
 
+#define ELF64_R_SYM(info) ((info)>>32)
+#define ELF64_R_TYPE(info) ((Elf64_Word)(info))
+#define ELF64_R_INFO(sym, type) (((Elf64_Xword)(sym)<<32)+(Elf64_Xword)(type))
+
+#define R_AMD64_RELATIVE 8
+
+struct Elf64_Rel
+{
+    Elf64_Addr r_offset;
+    Elf64_Xword r_info;
+};
+
+struct Elf64_Rela
+{
+    Elf64_Addr r_offset;
+    Elf64_Xword r_info;
+    Elf64_Sxword r_addend;
+};
+
diff --git a/api/loader/efi/shim.h b/api/loader/efi/shim.h
index 3486c34..9421cc3 100644
--- a/api/loader/efi/shim.h
+++ b/api/loader/efi/shim.h
@@ -13,8 +13,6 @@
 #define OsVendorMemoryType(t) ((EFI_MEMORY_TYPE)(0x80000000|t))
 #define SystemMemoryType OsVendorMemoryType(1)
 
-struct efi_loader_image;
-
 struct efi_loader_image
 {
     CHAR16 *path;
diff --git a/debug.sh b/debug.sh
index 1d606af..eacdc94 100755
--- a/debug.sh
+++ b/debug.sh
@@ -1,6 +1,7 @@
 #!/usr/bin/env bash
 
 make -C loader &&
+make -C shim &&
 make -C kernel &&
 
 ./image.sh &&
diff --git a/efi.mk b/efi.mk
index 72bd136..4067e44 100644
--- a/efi.mk
+++ b/efi.mk
@@ -22,7 +22,7 @@ CPPFLAGS += -I$(EFIAPIDIR) -I$(EFIAPIDIR)/protocol -I$(EFIAPIDIR)/$(GNUEFIARCH)
             -DGNU_EFI_USE_MS_ABI -DEFI_CALL_WRAPPER -DEFI_DEBUG
 
 CFLAGS += -fPIC -fshort-wchar -maccumulate-outgoing-args -mno-avx -mno-sse \
-          -mno-mmx
+          -mno-mmx -funsigned-char -Wno-pointer-sign
 
 OBJCOPY.efi = $(OBJCOPY) -j .text -j .sdata -j .data -j .dynamic \
 			-j .dynsm -j .rel -j .rela -j .reloc \
diff --git a/image.sh b/image.sh
index 7d32df4..a14f635 100755
--- a/image.sh
+++ b/image.sh
@@ -2,6 +2,7 @@
 
 imagefile=uefi.img
 loaderfile=loader/loader.efi
+shimfile=shim/efi.os
 kernelfile=kernel/kernel.os
 
 if [[ ! -f ${imagefile} ]]; then
@@ -14,5 +15,6 @@ mmd -i ${imagefile} -Do ::EFI/BOOT
 mcopy -i ${imagefile} -Do ${loaderfile} ::EFI/BOOT/BOOTX64.EFI
 mmd -i ${imagefile} -Do ::adasoft
 mmd -i ${imagefile} -Do ::adasoft/sophia
-mcopy -i ${imagefile} ${kernelfile} -Do ::adasoft/sophia
+mcopy -i ${imagefile} -Do ${shimfile} -Do ::adasoft/sophia
+mcopy -i ${imagefile} -Do ${kernelfile} -Do ::adasoft/sophia
 
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;
+        }
+    }
+}
+
diff --git a/lib/elf.h b/lib/elf.h
new file mode 100644
index 0000000..3edb0a1
--- /dev/null
+++ b/lib/elf.h
@@ -0,0 +1,17 @@
+#pragma once
+
+#include <elf/elf64.h>
+
+#include <stdbool.h>
+#include <stddef.h>
+
+#ifdef __x86_64__
+# define elf_validate elf64_validate
+# define elf_size elf64_size
+# define elf_reloc elf64_reloc
+#endif
+
+bool elf64_validate(Elf64_Ehdr *ehdr, unsigned type, unsigned machine);
+size_t elf64_size(Elf64_Ehdr *ehdr, Elf64_Phdr *phdr);
+void elf64_reloc(Elf64_Ehdr *ehdr);
+
diff --git a/loader/main_efi.c b/loader/main_efi.c
index 7edb44d..4c9c9a0 100644
--- a/loader/main_efi.c
+++ b/loader/main_efi.c
@@ -145,7 +145,8 @@ EFI_STATUS open_image(struct efi_loader_image *image)
                         &ehdr_size, 
                         &ehdr))))
     {
-        if (elf_validate(&ehdr, ET_EXEC, EM_X86_64))
+        if (elf_validate(&ehdr, ET_EXEC, EM_X86_64) ||
+                elf_validate(&ehdr, ET_DYN, EM_X86_64))
         {
             phdrs_size = ehdr.e_phentsize * ehdr.e_phnum;
             phdrs = AllocatePool(phdrs_size);
diff --git a/shim/Makefile b/shim/Makefile
index 51ec96c..42007b8 100644
--- a/shim/Makefile
+++ b/shim/Makefile
@@ -15,11 +15,11 @@ CFLAGS += -Wno-unused-const-variable -Wno-unused-function -fvisibility=hidden \
 
 LIBDIRS += -L$(dir $(shell $(CC) -print-libgcc-file-name))
 LDSCRIPT := shim.ld
-LDFLAGS += -z max-page-size=4096 --export-dynamic
+LDFLAGS += -z max-page-size=4096 --export-dynamic -pic --no-dynamic-linker
 LOADLIBES := -lgcc
 
-OBJS := entry.o memcmp.o memcpy.o memmove.o memset.o
-$(OBJS): CFLAGS += -fPIC -fPIE
+OBJS := entry.o elf.o memcmp.o memcpy.o memmove.o memset.o
+$(OBJS): CFLAGS += -fPIC
 
 DEPS := $(patsubst %.o,%.d,$(OBJS))
 
diff --git a/shim/entry.c b/shim/entry.c
index 303f582..a4d00c7 100644
--- a/shim/entry.c
+++ b/shim/entry.c
@@ -49,7 +49,11 @@ EFI_STATUS efi_shim_entry(struct efi_loader_image *image,
      * 3. exit boot services
      * 5. ???????????
      */
-    
+
+    void *image_base = (void *)image->buffer_base;
+
+    elf_reloc(image_base);
+
     EFI_STATUS status;
 
     if (!image)