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[Xen-devel] [PATCH v2] x86/EFI: use less crude a way of generating the build ID

Recent enough binutils (2.25 onwards) support --build-id also for
COFF/PE output, and hence we should use that in favor of the original
hack when possible.

This gets complicated by the linker requiring at least one COFF object
file to attach the .buildid section to. Hence the patch introduces a
buildid.ihex (in order to avoid introducing binary files into the repo)
which then gets converted to a binary minimal COFF object (no sections,
no symbols).

Also (to avoid both code fragment going out of sync) remove an unneeded
ALIGN() from xen.lds.S: Adding an equivalent of it to the .buildid
section would cause the _erodata symbol to become associated with the
wrong section again (see commit 0970299de5 ["x86/EFI + Live Patch:
avoid symbol address truncation"]). And it's pointless because the
alignment already gets properly set by the input section(s).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
v2: Fix --build-id support detection: Only pass -m option (some of the
    others result in an error message confusing ld-ver-build-id).
---
Question of course is whether consumers of the build ID other than Xen
itself need to be taught how to find it in an EFI binary.

--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -158,24 +158,30 @@ $(TARGET).efi: VIRT_BASE = 0x$(shell $(N
 $(TARGET).efi: ALT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A 
ALT_START$$,,p')
 # Don't use $(wildcard ...) here - at least make 3.80 expands this too early!
 $(TARGET).efi: guard = $(if $(shell echo efi/dis* | grep disabled),:)
+
 ifneq ($(build_id_linker),)
-$(TARGET).efi: note.o
+ifeq ($(call ld-ver-build-id,$(LD) $(filter -m%,$(EFI_LDFLAGS))),y)
+CFLAGS += -DBUILD_ID_EFI
+EFI_LDFLAGS += $(build_id_linker)
+note_file := efi/buildid.o
+else
 note_file := note.o
+endif
 else
 note_file :=
 endif
 
-$(TARGET).efi: prelink-efi.o efi.lds efi/relocs-dummy.o 
$(BASEDIR)/common/symbols-dummy.o efi/mkreloc
+$(TARGET).efi: prelink-efi.o $(note_file) efi.lds efi/relocs-dummy.o 
$(BASEDIR)/common/symbols-dummy.o efi/mkreloc
        $(foreach base, $(VIRT_BASE) $(ALT_BASE), \
                  $(guard) $(LD) $(call EFI_LDFLAGS,$(base)) -T efi.lds -N $< 
efi/relocs-dummy.o \
-                       $(BASEDIR)/common/symbols-dummy.o -o 
$(@D)/.$(@F).$(base).0 &&) :
+                       $(BASEDIR)/common/symbols-dummy.o $(note_file) -o 
$(@D)/.$(@F).$(base).0 &&) :
        $(guard) efi/mkreloc $(foreach base,$(VIRT_BASE) 
$(ALT_BASE),$(@D)/.$(@F).$(base).0) >$(@D)/.$(@F).0r.S
        $(guard) $(NM) -pa --format=sysv $(@D)/.$(@F).$(VIRT_BASE).0 \
                | $(guard) $(BASEDIR)/tools/symbols $(all_symbols) --sysv 
--sort >$(@D)/.$(@F).0s.S
        $(guard) $(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).0r.o 
$(@D)/.$(@F).0s.o
        $(foreach base, $(VIRT_BASE) $(ALT_BASE), \
                  $(guard) $(LD) $(call EFI_LDFLAGS,$(base)) -T efi.lds -N $< \
-                       $(@D)/.$(@F).0r.o $(@D)/.$(@F).0s.o -o 
$(@D)/.$(@F).$(base).1 &&) :
+                       $(@D)/.$(@F).0r.o $(@D)/.$(@F).0s.o $(note_file) -o 
$(@D)/.$(@F).$(base).1 &&) :
        $(guard) efi/mkreloc $(foreach base,$(VIRT_BASE) 
$(ALT_BASE),$(@D)/.$(@F).$(base).1) >$(@D)/.$(@F).1r.S
        $(guard) $(NM) -pa --format=sysv $(@D)/.$(@F).$(VIRT_BASE).1 \
                | $(guard) $(BASEDIR)/tools/symbols $(all_symbols) --sysv 
--sort >$(@D)/.$(@F).1s.S
@@ -185,8 +191,8 @@ $(TARGET).efi: prelink-efi.o efi.lds efi
        if $(guard) false; then rm -f $@; echo 'EFI support disabled'; fi
        rm -f $(@D)/.$(@F).[0-9]*
 
-efi/boot.init.o efi/runtime.o efi/compat.o: $(BASEDIR)/arch/x86/efi/built_in.o
-efi/boot.init.o efi/runtime.o efi/compat.o: ;
+efi/boot.init.o efi/runtime.o efi/compat.o efi/buildid.o: 
$(BASEDIR)/arch/x86/efi/built_in.o
+efi/boot.init.o efi/runtime.o efi/compat.o efi/buildid.o: ;
 
 asm-offsets.s: $(TARGET_SUBARCH)/asm-offsets.c
        $(CC) $(filter-out -flto,$(CFLAGS)) -S -o $@ $<
--- a/xen/arch/x86/efi/Makefile
+++ b/xen/arch/x86/efi/Makefile
@@ -9,6 +9,9 @@ efi := $(if $(efi),$(shell $(CC) $(filte
 efi := $(if $(efi),$(shell $(LD) -mi386pep --subsystem=10 -o check.efi check.o 
2>disabled && echo y))
 efi := $(if $(efi),$(shell rm disabled)y,$(shell $(call create,boot.init.o); 
$(call create,runtime.o)))
 
-extra-$(efi) += boot.init.o relocs-dummy.o runtime.o compat.o
+extra-$(efi) += boot.init.o relocs-dummy.o runtime.o compat.o buildid.o
+
+%.o: %.ihex
+       $(OBJCOPY) -I ihex -O binary $< $@
 
 stub.o: $(extra-y)
--- /dev/null
+++ b/xen/arch/x86/efi/buildid.ihex
@@ -0,0 +1,3 @@
+:10000000648600004D8DAD57140000000000000014
+:0400100000000000EC
+:00000001FF
--- a/xen/arch/x86/efi/mkreloc.c
+++ b/xen/arch/x86/efi/mkreloc.c
@@ -342,6 +342,7 @@ int main(int argc, char *argv[])
          */
         if ( memcmp(sec1[i].name, ".initcal", sizeof(sec1[i].name)) == 0 ||
              memcmp(sec1[i].name, ".init.se", sizeof(sec1[i].name)) == 0 ||
+             memcmp(sec1[i].name, ".buildid", sizeof(sec1[i].name)) == 0 ||
              memcmp(sec1[i].name, ".lockpro", sizeof(sec1[i].name)) == 0 )
             continue;
 
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -93,7 +93,7 @@ SECTIONS
        *(.rodata)
        *(.rodata.*)
 
-#if defined(BUILD_ID) && defined(EFI)
+#if defined(BUILD_ID) && defined(EFI) && !defined(BUILD_ID_EFI)
 /*
  * No mechanism to put an PT_NOTE in the EFI file - so put
  * it in .rodata section. (notes.o supplies us with .note.gnu.build-id).
@@ -122,19 +122,26 @@ SECTIONS
 #endif
   } :text
 
-#if defined(BUILD_ID) && !defined(EFI)
+#if defined(BUILD_ID)
+#if !defined(EFI)
 /*
  * What a strange section name. The reason is that on ELF builds this section
  * is extracted to notes.o (which then is ingested in the EFI file). But the
  * compiler may want to inject other things in the .note which we don't care
  * about - hence this unique name.
  */
-  . = ALIGN(4);
   .note.gnu.build-id : {
        __note_gnu_build_id_start = .;
        *(.note.gnu.build-id)
        __note_gnu_build_id_end = .;
   } :note :text
+#elif defined(BUILD_ID_EFI)
+  .buildid : {
+       __note_gnu_build_id_start = .;
+       *(.buildid)
+       __note_gnu_build_id_end = .;
+  } :text
+#endif
 #endif
   _erodata = .;
 
--- a/xen/common/version.c
+++ b/xen/common/version.c
@@ -4,6 +4,7 @@
 #include <xen/lib.h>
 #include <xen/string.h>
 #include <xen/types.h>
+#include <xen/efi.h>
 #include <xen/elf.h>
 #include <xen/version.h>
 
@@ -117,10 +118,33 @@ int xen_build_id_check(const Elf_Note *n
     return 0;
 }
 
+struct pe_external_debug_directory
+{
+    uint32_t characteristics;
+    uint32_t time_stamp;
+    uint16_t major_version;
+    uint16_t minor_version;
+#define PE_IMAGE_DEBUG_TYPE_CODEVIEW 2
+    uint32_t type;
+    uint32_t size;
+    uint32_t rva_of_data;
+    uint32_t filepos_of_data;
+};
+
+struct cv_info_pdb70
+{
+#define CVINFO_PDB70_CVSIGNATURE 0x53445352 /* "RSDS" */
+    uint32_t cv_signature;
+    unsigned char signature[16];
+    uint32_t age;
+    char pdb_filename[];
+};
+
 static int __init xen_build_init(void)
 {
     const Elf_Note *n = __note_gnu_build_id_start;
     unsigned int sz;
+    int rc;
 
     /* --build-id invoked with wrong parameters. */
     if ( __note_gnu_build_id_end <= &n[0] )
@@ -132,7 +156,38 @@ static int __init xen_build_init(void)
 
     sz = (void *)__note_gnu_build_id_end - (void *)n;
 
-    return xen_build_id_check(n, sz, &build_id_p, &build_id_len);
+    rc = xen_build_id_check(n, sz, &build_id_p, &build_id_len);
+
+#ifdef CONFIG_X86
+    /* Alternatively we may have a CodeView record from an EFI build. */
+    if ( rc && efi_enabled )
+    {
+        const struct pe_external_debug_directory *dir = (const void *)n;
+
+        /*
+         * Validate that the full-note-header check above won't prevent
+         * fall-through to the CodeView case here.
+         */
+        BUILD_BUG_ON(sizeof(*n) > sizeof(*dir));
+
+        if ( sz > sizeof(*dir) + sizeof(struct cv_info_pdb70) &&
+             dir->type == PE_IMAGE_DEBUG_TYPE_CODEVIEW &&
+             dir->size > sizeof(struct cv_info_pdb70) &&
+             XEN_VIRT_START + dir->rva_of_data == (unsigned long)(dir + 1) )
+        {
+            const struct cv_info_pdb70 *info = (const void *)(dir + 1);
+
+            if ( info->cv_signature == CVINFO_PDB70_CVSIGNATURE )
+            {
+                build_id_p = info->signature;
+                build_id_len = sizeof(info->signature);
+                rc = 0;
+            }
+        }
+    }
+#endif
+
+    return rc;
 }
 __initcall(xen_build_init);
 #endif

Attachment: x86-EFI-build-ID.patch
Description: Text document

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