[PATCH 4/7] x86/boot: apply trampoline relocations at destination position

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Change the order relocations are applied.  Currently the trampoline is
patched for relocations before being copied to the low 1MB region.  Change
the order and instead copy the trampoline first to the low 1MB region and
then apply the relocations.

This will allow making .init.text section read-only (so read and execute
permissions only), which is relevant when Xen is built as a PE image.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/boot/build32.lds.S      |  1 +
 xen/arch/x86/boot/head.S             |  6 +++---
 xen/arch/x86/boot/reloc-trampoline.c | 16 ++++++++--------
 xen/arch/x86/efi/efi-boot.h          | 15 ++++++---------
 4 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/xen/arch/x86/boot/build32.lds.S b/xen/arch/x86/boot/build32.lds.S
index 1e59732edd6e..92dc320b7380 100644
--- a/xen/arch/x86/boot/build32.lds.S
+++ b/xen/arch/x86/boot/build32.lds.S
@@ -50,6 +50,7 @@ SECTIONS
         DECLARE_IMPORT(__trampoline_seg_start);
         DECLARE_IMPORT(__trampoline_seg_stop);
         DECLARE_IMPORT(trampoline_phys);
+        DECLARE_IMPORT(trampoline_start);
         DECLARE_IMPORT(boot_vid_info);
         . = . + GAP;
         *(.text)
diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index 59a2b5005cf6..3f81b21b5a7f 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -679,9 +679,6 @@ trampoline_setup:
         shr     $PAGE_SHIFT, %ecx                /* %ecx = Slot to write */
         mov     %edx, sym_offs(l1_bootmap)(%esi, %ecx, 8)
 
-        /* Apply relocations to bootstrap trampoline. */
-        call    reloc_trampoline32
-
         /* Do not parse command line on EFI platform here. */
         cmpb    $0, sym_esi(efi_platform)
         jnz     1f
@@ -709,6 +706,9 @@ trampoline_setup:
         mov     $((trampoline_end - trampoline_start) / 4),%ecx
         rep movsl
 
+        /* Apply relocations to bootstrap trampoline. */
+        call    reloc_trampoline32
+
         /* Jump into the relocated trampoline. */
         lret
 
diff --git a/xen/arch/x86/boot/reloc-trampoline.c 
b/xen/arch/x86/boot/reloc-trampoline.c
index e35e7c78aa86..ac54aef14eaf 100644
--- a/xen/arch/x86/boot/reloc-trampoline.c
+++ b/xen/arch/x86/boot/reloc-trampoline.c
@@ -20,19 +20,19 @@ void reloc_trampoline64(void)
     uint32_t phys = trampoline_phys;
     const int32_t *trampoline_ptr;
 
-    /*
-     * Apply relocations to trampoline.
-     *
-     * This modifies the trampoline in place within Xen, so that it will
-     * operate correctly when copied into place.
-     */
+    /* Apply relocations to trampoline after copy to destination. */
+#define RELA_TARGET(ptr, bits) \
+    *(uint ## bits ## _t *)(phys + *ptr + (long)ptr - (long)trampoline_start)
+
     for ( trampoline_ptr = __trampoline_rel_start;
           trampoline_ptr < __trampoline_rel_stop;
           ++trampoline_ptr )
-        *(uint32_t *)(*trampoline_ptr + (long)trampoline_ptr) += phys;
+        RELA_TARGET(trampoline_ptr, 32) += phys;
 
     for ( trampoline_ptr = __trampoline_seg_start;
           trampoline_ptr < __trampoline_seg_stop;
           ++trampoline_ptr )
-        *(uint16_t *)(*trampoline_ptr + (long)trampoline_ptr) = phys >> 4;
+        RELA_TARGET(trampoline_ptr, 16) = phys >> 4;
+
+#undef RELA_TARGET
 }
diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index 1d8902a9a724..e4ed8639b9ac 100644
--- a/xen/arch/x86/efi/efi-boot.h
+++ b/xen/arch/x86/efi/efi-boot.h
@@ -105,10 +105,8 @@ static void __init efi_arch_relocate_image(unsigned long 
delta)
     }
 }
 
-static void __init relocate_trampoline(unsigned long phys)
+static void __init relocate_trampoline(void)
 {
-    trampoline_phys = phys;
-
     if ( !efi_enabled(EFI_LOADER) )
         return;
 
@@ -213,6 +211,8 @@ static void __init 
efi_arch_process_memory_map(EFI_SYSTEM_TABLE *SystemTable,
         }
     }
 
+    if ( !trampoline_phys )
+        trampoline_phys = cfg.addr;
 }
 
 static void *__init efi_arch_allocate_mmap_buffer(UINTN map_size)
@@ -223,11 +223,7 @@ static void *__init efi_arch_allocate_mmap_buffer(UINTN 
map_size)
 static void __init efi_arch_pre_exit_boot(void)
 {
     if ( !trampoline_phys )
-    {
-        if ( !cfg.addr )
-            blexit(L"No memory for trampoline");
-        relocate_trampoline(cfg.addr);
-    }
+        blexit(L"No memory for trampoline");
 }
 
 static void __init noreturn efi_arch_post_exit_boot(void)
@@ -236,6 +232,7 @@ static void __init noreturn efi_arch_post_exit_boot(void)
 
     efi_arch_relocate_image(__XEN_VIRT_START - xen_phys_start);
     memcpy(_p(trampoline_phys), trampoline_start, cfg.size);
+    relocate_trampoline();
 
     /*
      * We're in physical mode right now (i.e. identity map), so a regular
@@ -638,7 +635,7 @@ static void __init efi_arch_memory_setup(void)
     status = efi_bs->AllocatePages(AllocateMaxAddress, EfiLoaderData,
                                    PFN_UP(cfg.size), &cfg.addr);
     if ( status == EFI_SUCCESS )
-        relocate_trampoline(cfg.addr);
+        trampoline_phys = cfg.addr;
     else
     {
         cfg.addr = 0;
-- 
2.48.1