[PATCH v2 5/8] KVM: arm64: Apply hyp relocations at runtime

David Brazdil
2021-01-05T18:06:49Z

KVM nVHE code runs under a different VA mapping than the kernel, hence
so far it avoided using absolute addressing because the VA in a constant
pool is relocated by the linker to a kernel VA (see hyp_symbol_addr).

Now the kernel has access to a list of positions that contain a kimg VA
but will be accessed only in hyp execution context. These are generated
by the gen-hyprel build-time tool and stored in .hyp.reloc.

Add early boot pass over the entries and convert the kimg VAs to hyp VAs.
Note that this requires for .hyp* ELF sections to be mapped read-write
at that point.

Signed-off-by: David Brazdil <dbrazdil@google.com>
---
arch/arm64/include/asm/kvm_mmu.h | 1 +
arch/arm64/include/asm/sections.h | 1 +
arch/arm64/kernel/smp.c | 4 +++-
arch/arm64/kvm/va_layout.c | 28 ++++++++++++++++++++++++++++
4 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index e52d82aeadca..6bbb44011c84 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -129,6 +129,7 @@ alternative_cb_end
void kvm_update_va_mask(struct alt_instr *alt,
__le32 *origptr, __le32 *updptr, int nr_inst);
void kvm_compute_layout(void);
+void kvm_apply_hyp_relocations(void);

static __always_inline unsigned long __kern_hyp_va(unsigned long v)
{
diff --git a/arch/arm64/include/asm/sections.h b/arch/arm64/include/asm/sections.h
index a6f3557d1ab2..2f36b16a5b5d 100644
--- a/arch/arm64/include/asm/sections.h
+++ b/arch/arm64/include/asm/sections.h
@@ -12,6 +12,7 @@ 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_rodata_start[], __hyp_rodata_end[];
+extern char __hyp_reloc_begin[], __hyp_reloc_end[];
extern char __idmap_text_start[], __idmap_text_end[];
extern char __initdata_begin[], __initdata_end[];
extern char __inittext_begin[], __inittext_end[];
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index d08948c6979b..006f61a86438 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -434,8 +434,10 @@ static void __init hyp_mode_check(void)
"CPU: CPUs started in inconsistent modes");
else
pr_info("CPU: All CPU(s) started at EL1\n");
- if (IS_ENABLED(CONFIG_KVM) && !is_kernel_in_hyp_mode())
+ if (IS_ENABLED(CONFIG_KVM) && !is_kernel_in_hyp_mode()) {
kvm_compute_layout();
+ kvm_apply_hyp_relocations();
+ }
}

void __init smp_cpus_done(unsigned int max_cpus)
diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c
index 70fcd6a12fe1..fee7dcd95d73 100644
--- a/arch/arm64/kvm/va_layout.c
+++ b/arch/arm64/kvm/va_layout.c
@@ -81,6 +81,34 @@ __init void kvm_compute_layout(void)
init_hyp_physvirt_offset();
}

+/*
+ * The .hyp.reloc ELF section contains a list of kimg positions that
+ * contains kimg VAs but will be accessed only in hyp execution context.
+ * Convert them to hyp VAs. See gen-hyprel.c for more details.
+ */
+__init void kvm_apply_hyp_relocations(void)
+{
+ int32_t *rel;
+ int32_t *begin = (int32_t *)__hyp_reloc_begin;
+ int32_t *end = (int32_t *)__hyp_reloc_end;
+
+ for (rel = begin; rel < end; ++rel) {
+ uintptr_t *ptr, kimg_va;
+
+ /*
+ * Each entry contains a 32-bit relative offset from itself
+ * to a kimg VA position.
+ */
+ ptr = (uintptr_t *)lm_alias((char *)rel + *rel);
+
+ /* Read the kimg VA value at the relocation address. */
+ kimg_va = *ptr;
+
+ /* Convert to hyp VA and store back to the relocation address. */
+ *ptr = __early_kern_hyp_va((uintptr_t)lm_alias(kimg_va));
+ }
+}
+
static u32 compute_instruction(int n, u32 rd, u32 rn)
{
u32 insn = AARCH64_BREAK_FAULT;
--
2.29.2.729.g45daf8777d-goog