3 files changed, 29 insertions, 28 deletions

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f40bdf97d390..ed04a968cc7d 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1525,7 +1525,9 @@ SYM_CODE_END(rewind_stack_and_make_dead)
  * ORC to unwind properly.
  *
  * The alignment is for performance and not for safety, and may be safely
- * refactored in the future if needed.
+ * refactored in the future if needed. The .skips are for safety, to ensure
+ * that all RETs are in the second half of a cacheline to mitigate Indirect
+ * Target Selection, rather than taking the slowpath via its_return_thunk.
  */
 SYM_FUNC_START(clear_bhb_loop)
 	ANNOTATE_NOENDBR
@@ -1536,10 +1538,22 @@ SYM_FUNC_START(clear_bhb_loop)
 	call	1f
 	jmp	5f
 	.align 64, 0xcc
+	/*
+	 * Shift instructions so that the RET is in the upper half of the
+	 * cacheline and don't take the slowpath to its_return_thunk.
+	 */
+	.skip 32 - (.Lret1 - 1f), 0xcc
 	ANNOTATE_INTRA_FUNCTION_CALL
 1:	call	2f
-	RET
+.Lret1:	RET
 	.align 64, 0xcc
+	/*
+	 * As above shift instructions for RET at .Lret2 as well.
+	 *
+	 * This should be ideally be: .skip 32 - (.Lret2 - 2f), 0xcc
+	 * but some Clang versions (e.g. 18) don't like this.
+	 */
+	.skip 32 - 18, 0xcc
 2:	movl	$5, %eax
 3:	jmp	4f
 	nop
@@ -1547,7 +1561,7 @@ SYM_FUNC_START(clear_bhb_loop)
 	jnz	3b
 	sub	$1, %ecx
 	jnz	1b
-	RET
+.Lret2:	RET
 5:	lfence
 	pop	%rbp
 	RET
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index adb299d3b6a1..afe105b2f907 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -65,7 +65,6 @@ static vm_fault_t vdso_fault(const struct vm_special_mapping *sm,
 static void vdso_fix_landing(const struct vdso_image *image,
 		struct vm_area_struct *new_vma)
 {
-#if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
 	if (in_ia32_syscall() && image == &vdso_image_32) {
 		struct pt_regs *regs = current_pt_regs();
 		unsigned long vdso_land = image->sym_int80_landing_pad;
@@ -76,7 +75,6 @@ static void vdso_fix_landing(const struct vdso_image *image,
 		if (regs->ip == old_land_addr)
 			regs->ip = new_vma->vm_start + vdso_land;
 	}
-#endif
 }
 
 static int vdso_mremap(const struct vm_special_mapping *sm,
@@ -227,7 +225,6 @@ int map_vdso_once(const struct vdso_image *image, unsigned long addr)
 	return map_vdso(image, addr);
 }
 
-#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 static int load_vdso32(void)
 {
 	if (vdso32_enabled != 1)  /* Other values all mean "disabled" */
@@ -235,45 +232,38 @@ static int load_vdso32(void)
 
 	return map_vdso(&vdso_image_32, 0);
 }
-#endif
 
-#ifdef CONFIG_X86_64
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
-	if (!vdso64_enabled)
-		return 0;
+	if (IS_ENABLED(CONFIG_X86_64)) {
+		if (!vdso64_enabled)
+			return 0;
+
+		return map_vdso(&vdso_image_64, 0);
+	}
 
-	return map_vdso(&vdso_image_64, 0);
+	return load_vdso32();
 }
 
 #ifdef CONFIG_COMPAT
 int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
 				       int uses_interp, bool x32)
 {
-#ifdef CONFIG_X86_X32_ABI
-	if (x32) {
+	if (IS_ENABLED(CONFIG_X86_X32_ABI) && x32) {
 		if (!vdso64_enabled)
 			return 0;
 		return map_vdso(&vdso_image_x32, 0);
 	}
-#endif
-#ifdef CONFIG_IA32_EMULATION
-	return load_vdso32();
-#else
+
+	if (IS_ENABLED(CONFIG_IA32_EMULATION))
+		return load_vdso32();
+
 	return 0;
-#endif
-}
-#endif
-#else
-int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
-{
-	return load_vdso32();
 }
 #endif
 
 bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
 {
-#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 	const struct vdso_image *image = current->mm->context.vdso_image;
 	unsigned long vdso = (unsigned long) current->mm->context.vdso;
 
@@ -282,7 +272,6 @@ bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
 		    regs->ip == vdso + image->sym_vdso32_rt_sigreturn_landing_pad)
 			return true;
 	}
-#endif
 	return false;
 }
 
diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index 2fb7d53cf333..c9103a6fa06e 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -341,9 +341,7 @@ void __init set_vsyscall_pgtable_user_bits(pgd_t *root)
 	pgd = pgd_offset_pgd(root, VSYSCALL_ADDR);
 	set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));
 	p4d = p4d_offset(pgd, VSYSCALL_ADDR);
-#if CONFIG_PGTABLE_LEVELS >= 5
 	set_p4d(p4d, __p4d(p4d_val(*p4d) | _PAGE_USER));
-#endif
 	pud = pud_offset(p4d, VSYSCALL_ADDR);
 	set_pud(pud, __pud(pud_val(*pud) | _PAGE_USER));
 	pmd = pmd_offset(pud, VSYSCALL_ADDR);