KVM: arm64: Add .hyp.data..ro_after_init ELF section

Add rules for renaming the .data..ro_after_init ELF section in KVM nVHE
object files to .hyp.data..ro_after_init, linking it into the kernel
and mapping it in hyp at runtime.

The section is RW to the host, then mapped RO in hyp. The expectation is
that the host populates the variables in the section and they are never
changed by hyp afterwards.

Signed-off-by: David Brazdil <dbrazdil@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201202184122.26046-13-dbrazdil@google.com

arch/arm64/include/asm/sections.h

@@ -11,6 +11,7 @@ extern char __alt_instructions[], __alt_instructions_end[];
 extern char __hibernate_exit_text_start[], __hibernate_exit_text_end[];
 extern char __hyp_idmap_text_start[], __hyp_idmap_text_end[];
 extern char __hyp_text_start[], __hyp_text_end[];
+extern char __hyp_data_ro_after_init_start[], __hyp_data_ro_after_init_end[];
 extern char __idmap_text_start[], __idmap_text_end[];
 extern char __initdata_begin[], __initdata_end[];
 extern char __inittext_begin[], __inittext_end[];

arch/arm64/kernel/vmlinux.lds.S

@@ -30,6 +30,13 @@ jiffies = jiffies_64;
 	*(__kvm_ex_table)					\
 	__stop___kvm_ex_table = .;
 
+#define HYPERVISOR_DATA_SECTIONS				\
+	HYP_SECTION_NAME(.data..ro_after_init) : {		\
+		__hyp_data_ro_after_init_start = .;		\
+		*(HYP_SECTION_NAME(.data..ro_after_init))	\
+		__hyp_data_ro_after_init_end = .;		\
+	}
+
 #define HYPERVISOR_PERCPU_SECTION				\
 	. = ALIGN(PAGE_SIZE);					\
 	HYP_SECTION_NAME(.data..percpu) : {			\
@@ -37,6 +44,7 @@ jiffies = jiffies_64;
 	}
 #else /* CONFIG_KVM */
 #define HYPERVISOR_EXTABLE
+#define HYPERVISOR_DATA_SECTIONS
 #define HYPERVISOR_PERCPU_SECTION
 #endif
 
@@ -234,6 +242,8 @@ SECTIONS
 	_sdata = .;
 	RW_DATA(L1_CACHE_BYTES, PAGE_SIZE, THREAD_ALIGN)
 
+	HYPERVISOR_DATA_SECTIONS
+
 	/*
 	 * Data written with the MMU off but read with the MMU on requires
 	 * cache lines to be invalidated, discarding up to a Cache Writeback

arch/arm64/kvm/arm.c

@@ -1627,6 +1627,14 @@ static int init_hyp_mode(void)
 		goto out_err;
 	}
 
+	err = create_hyp_mappings(kvm_ksym_ref(__hyp_data_ro_after_init_start),
+				  kvm_ksym_ref(__hyp_data_ro_after_init_end),
+				  PAGE_HYP_RO);
+	if (err) {
+		kvm_err("Cannot map .hyp.data..ro_after_init section\n");
+		goto out_err;
+	}
+
 	err = create_hyp_mappings(kvm_ksym_ref(__start_rodata),
 				  kvm_ksym_ref(__end_rodata), PAGE_HYP_RO);
 	if (err) {

arch/arm64/kvm/hyp/nvhe/hyp.lds.S

@@ -16,4 +16,5 @@ SECTIONS {
 	HYP_SECTION_NAME(.data..percpu) : {
 		PERCPU_INPUT(L1_CACHE_BYTES)
 	}
+	HYP_SECTION(.data..ro_after_init)
 }