[v7] x86: strict separation of startup code

[PATCH v7 16/22] x86/boot: Check startup code for absence of absolute relocations

Posted by Ard Biesheuvel 1 week, 3 days ago

From: Ard Biesheuvel <ardb@kernel.org>

Invoke objtool on each startup code object individually to check for the
absence of absolute relocations. This is needed because this code will
be invoked from the 1:1 mapping of memory before those absolute virtual
addresses (which are derived from the kernel virtual base address
provided to the linker and possibly shifted at boot) are mapped.

Only objects built under arch/x86/boot/startup/ have this restriction,
and once they have been incorporated into vmlinux.o, this distinction is
difficult to make. So force the invocation of objtool for each object
file individually, even if objtool is deferred to vmlinux.o for the rest
of the build. In the latter case, only pass --noabs and nothing else;
otherwise, append it to the existing objtool command line.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/boot/startup/Makefile | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/boot/startup/Makefile b/arch/x86/boot/startup/Makefile
index b514f7e81332..32737f4ab5a8 100644
--- a/arch/x86/boot/startup/Makefile
+++ b/arch/x86/boot/startup/Makefile
@@ -19,6 +19,7 @@ KCOV_INSTRUMENT	:= n
 
 obj-$(CONFIG_X86_64)		+= gdt_idt.o map_kernel.o
 obj-$(CONFIG_AMD_MEM_ENCRYPT)	+= sme.o sev-startup.o
+pi-objs				:= $(patsubst %.o,$(obj)/%.o,$(obj-y))
 
 lib-$(CONFIG_X86_64)		+= la57toggle.o
 lib-$(CONFIG_EFI_MIXED)		+= efi-mixed.o
@@ -28,3 +29,10 @@ lib-$(CONFIG_EFI_MIXED)		+= efi-mixed.o
 # to be linked into the decompressor or the EFI stub but not vmlinux
 #
 $(patsubst %.o,$(obj)/%.o,$(lib-y)): OBJECT_FILES_NON_STANDARD := y
+
+#
+# Invoke objtool for each object individually to check for absolute
+# relocations, even if other objtool actions are being deferred.
+#
+$(pi-objs): objtool-enabled	= 1
+$(pi-objs): objtool-args	= $(if $(delay-objtool),,$(objtool-args-y)) --noabs
-- 
2.51.0.268.g9569e192d0-goog

[tip: x86/sev] x86/boot: Check startup code for absence of absolute relocations

Posted by tip-bot2 for Ard Biesheuvel 3 days ago

The following commit has been merged into the x86/sev branch of tip:

Commit-ID:     296650c8ac4f18e886dd2a606152c00adf527219
Gitweb:        https://git.kernel.org/tip/296650c8ac4f18e886dd2a606152c00adf527219
Author:        Ard Biesheuvel <ardb@kernel.org>
AuthorDate:    Thu, 28 Aug 2025 12:22:19 +02:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Wed, 03 Sep 2025 17:59:54 +02:00

x86/boot: Check startup code for absence of absolute relocations

Invoke objtool on each startup code object individually to check for the
absence of absolute relocations. This is needed because this code will
be invoked from the 1:1 mapping of memory before those absolute virtual
addresses (which are derived from the kernel virtual base address
provided to the linker and possibly shifted at boot) are mapped.

Only objects built under arch/x86/boot/startup/ have this restriction,
and once they have been incorporated into vmlinux.o, this distinction is
difficult to make. So force the invocation of objtool for each object
file individually, even if objtool is deferred to vmlinux.o for the rest
of the build. In the latter case, only pass --noabs and nothing else;
otherwise, append it to the existing objtool command line.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250828102202.1849035-40-ardb+git@google.com
---
 arch/x86/boot/startup/Makefile | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/boot/startup/Makefile b/arch/x86/boot/startup/Makefile
index b514f7e..32737f4 100644
--- a/arch/x86/boot/startup/Makefile
+++ b/arch/x86/boot/startup/Makefile
@@ -19,6 +19,7 @@ KCOV_INSTRUMENT	:= n
 
 obj-$(CONFIG_X86_64)		+= gdt_idt.o map_kernel.o
 obj-$(CONFIG_AMD_MEM_ENCRYPT)	+= sme.o sev-startup.o
+pi-objs				:= $(patsubst %.o,$(obj)/%.o,$(obj-y))
 
 lib-$(CONFIG_X86_64)		+= la57toggle.o
 lib-$(CONFIG_EFI_MIXED)		+= efi-mixed.o
@@ -28,3 +29,10 @@ lib-$(CONFIG_EFI_MIXED)		+= efi-mixed.o
 # to be linked into the decompressor or the EFI stub but not vmlinux
 #
 $(patsubst %.o,$(obj)/%.o,$(lib-y)): OBJECT_FILES_NON_STANDARD := y
+
+#
+# Invoke objtool for each object individually to check for absolute
+# relocations, even if other objtool actions are being deferred.
+#
+$(pi-objs): objtool-enabled	= 1
+$(pi-objs): objtool-args	= $(if $(delay-objtool),,$(objtool-args-y)) --noabs