linux-kernel - [RFC PATCH 21/28] x86/head: Use PIC-compatible symbol references in startup code

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Message-ID: <20240925150059.3955569-51-ardb+git@google.com>
Date: Wed, 25 Sep 2024 17:01:21 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
	Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Uros Bizjak <ubizjak@...il.com>, 
	Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Vitaly Kuznetsov <vkuznets@...hat.com>, Juergen Gross <jgross@...e.com>, 
	Boris Ostrovsky <boris.ostrovsky@...cle.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arnd Bergmann <arnd@...db.de>, 
	Masahiro Yamada <masahiroy@...nel.org>, Kees Cook <kees@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Keith Packard <keithp@...thp.com>, 
	Justin Stitt <justinstitt@...gle.com>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, linux-doc@...r.kernel.org, 
	linux-pm@...r.kernel.org, kvm@...r.kernel.org, xen-devel@...ts.xenproject.org, 
	linux-efi@...r.kernel.org, linux-arch@...r.kernel.org, 
	linux-sparse@...r.kernel.org, linux-kbuild@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: [RFC PATCH 21/28] x86/head: Use PIC-compatible symbol references in
 startup code

From: Ard Biesheuvel <ardb@...nel.org>

Use RIP-relative symbol references to make them compatible with running
the linker in PIE mode.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/kernel/head_64.S            | 14 +++++++++-----
 arch/x86/kernel/relocate_kernel_64.S |  6 ++++--
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index db71cf64204b..cc2fec3de4b7 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -182,8 +182,9 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
 	xorl	%r15d, %r15d
 
 	/* Derive the runtime physical address of init_top_pgt[] */
-	movq	phys_base(%rip), %rax
-	addq	$(init_top_pgt - __START_KERNEL_map), %rax
+	leaq	init_top_pgt(%rip), %rax
+	subq	$__START_KERNEL_map, %rax
+	addq	phys_base(%rip), %rax
 
 	/*
 	 * Retrieve the modifier (SME encryption mask if SME is active) to be
@@ -314,7 +315,8 @@ SYM_INNER_LABEL(common_startup_64, SYM_L_LOCAL)
 
 .Lsetup_cpu:
 	/* Get the per cpu offset for the given CPU# which is in ECX */
-	movq	__per_cpu_offset(,%rcx,8), %rdx
+	leaq	__per_cpu_offset(%rip), %rdx
+	movq	(%rdx,%rcx,8), %rdx
 #else
 	xorl	%edx, %edx /* zero-extended to clear all of RDX */
 #endif /* CONFIG_SMP */
@@ -325,7 +327,8 @@ SYM_INNER_LABEL(common_startup_64, SYM_L_LOCAL)
 	 *
 	 * RDX contains the per-cpu offset
 	 */
-	movq	pcpu_hot + X86_current_task(%rdx), %rax
+	leaq	pcpu_hot + X86_current_task(%rip), %rax
+	movq	(%rax,%rdx), %rax
 	movq	TASK_threadsp(%rax), %rsp
 
 	/*
@@ -346,7 +349,8 @@ SYM_INNER_LABEL(common_startup_64, SYM_L_LOCAL)
 	 */
 	subq	$16, %rsp
 	movw	$(GDT_SIZE-1), (%rsp)
-	leaq	gdt_page(%rdx), %rax
+	leaq	gdt_page(%rip), %rax
+	addq	%rdx, %rax
 	movq	%rax, 2(%rsp)
 	lgdt	(%rsp)
 	addq	$16, %rsp
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index e9e88c342f75..cbfd0227ea3e 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -106,6 +106,9 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
 	/* setup a new stack at the end of the physical control page */
 	lea	PAGE_SIZE(%r8), %rsp
 
+	/* take the virtual address of virtual_mapped() before jumping */
+	leaq	virtual_mapped(%rip), %r14
+
 	/* jump to identity mapped page */
 	addq	$(identity_mapped - relocate_kernel), %r8
 	pushq	%r8
@@ -225,8 +228,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	movq	%rax, %cr3
 	lea	PAGE_SIZE(%r8), %rsp
 	call	swap_pages
-	movq	$virtual_mapped, %rax
-	pushq	%rax
+	pushq	%r14
 	ANNOTATE_UNRET_SAFE
 	ret
 	int3
-- 
2.46.0.792.g87dc391469-goog