[kvm-unit-tests PATCH v2 4/6] x86: efi_main: Self-relocate ELF .dynamic addresses

Varad Gautam
2021-08-19T11:35:18Z

EFI expects a relocatable PE, and the loader will patch in the
relocations from the COFF.

Since we are wrapping an ELF into a PE here, the EFI loader will
not handle ELF relocations, and we need to patch the ELF .dynamic
section manually on early boot.

Signed-off-by: Varad Gautam <varad.gautam@suse.com>
---
x86/efi_main.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 63 insertions(+)

diff --git a/x86/efi_main.c b/x86/efi_main.c
index 237d4e7..be3f9ab 100644
--- a/x86/efi_main.c
+++ b/x86/efi_main.c
@@ -1,9 +1,13 @@
#include <alloc_phys.h>
#include <linux/uefi.h>
+#include <elf.h>

unsigned long __efiapi efi_main(efi_handle_t handle, efi_system_table_t *sys_tab);
efi_system_table_t *efi_system_table = NULL;

+extern char ImageBase;
+extern char _DYNAMIC;
+
static void efi_free_pool(void *ptr)
{
efi_bs_call(free_pool, ptr);
@@ -93,11 +97,70 @@ static efi_status_t exit_efi(void *handle)
return EFI_SUCCESS;
}

+static efi_status_t elf_reloc(unsigned long image_base, unsigned long dynamic)
+{
+ long relsz = 0, relent = 0;
+ Elf64_Rel *rel = 0;
+ Elf64_Dyn *dyn = (Elf64_Dyn *) dynamic;
+ unsigned long *addr;
+ int i;
+
+ for (i = 0; dyn[i].d_tag != DT_NULL; i++) {
+ switch (dyn[i].d_tag) {
+ case DT_RELA:
+ rel = (Elf64_Rel *)
+ ((unsigned long) dyn[i].d_un.d_ptr + image_base);
+ break;
+ case DT_RELASZ:
+ relsz = dyn[i].d_un.d_val;
+ break;
+ case DT_RELAENT:
+ relent = dyn[i].d_un.d_val;
+ break;
+ default:
+ break;
+ }
+ }
+
+ if (!rel && relent == 0)
+ return EFI_SUCCESS;
+
+ if (!rel || relent == 0)
+ return EFI_LOAD_ERROR;
+
+ while (relsz > 0) {
+ /* apply the relocs */
+ switch (ELF64_R_TYPE (rel->r_info)) {
+ case R_X86_64_NONE:
+ break;
+ case R_X86_64_RELATIVE:
+ addr = (unsigned long *) (image_base + rel->r_offset);
+ *addr += image_base;
+ break;
+ default:
+ break;
+ }
+ rel = (Elf64_Rel *) ((char *) rel + relent);
+ relsz -= relent;
+ }
+ return EFI_SUCCESS;
+}
+
unsigned long __efiapi efi_main(efi_handle_t handle, efi_system_table_t *sys_tab)
{
+ unsigned long image_base, dyn;
efi_system_table = sys_tab;

exit_efi(handle);

+ image_base = (unsigned long) &ImageBase;
+ dyn = image_base + (unsigned long) &_DYNAMIC;
+
+ /* The EFI loader does not handle ELF relocations, so fixup
+ * .dynamic addresses before proceeding any further. */
+ elf_reloc(image_base, dyn);
+
+ start64();
+
return 0;
}
--
2.30.2