On 2020-11-19 16:25, David Brazdil wrote:
KVM nVHE code runs under a different VA mapping than the kernel, hence
so far it relied only on PC-relative addressing to avoid accidentally
using a relocated kernel VA from a constant pool (see hyp_symbol_addr).
So as to reduce the possibility of a programmer error, fixup the
relocated addresses instead. Let the kernel relocate them to kernel VA
first, but then iterate over them again, filter those that point to hyp
code/data and convert the kernel VA to hyp VA.
This is done after kvm_compute_layout and before apply_alternatives.
Signed-off-by: David Brazdil <dbraz...@google.com>
---
arch/arm64/include/asm/kvm_mmu.h | 1 +
arch/arm64/kernel/smp.c | 4 +-
arch/arm64/kvm/va_layout.c | 76 ++++++++++++++++++++++++++++++++
3 files changed, 80 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/kvm_mmu.h
b/arch/arm64/include/asm/kvm_mmu.h
index 5168a0c516ae..e5226f7e4732 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -105,6 +105,7 @@ 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_fixup_hyp_relocations(void);
static __always_inline unsigned long __kern_hyp_va(unsigned long v)
{
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 18e9727d3f64..30241afc2c93 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))
+ if (IS_ENABLED(CONFIG_KVM)) {
kvm_compute_layout();
+ kvm_fixup_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 d8cc51bd60bf..b80fab974896 100644
--- a/arch/arm64/kvm/va_layout.c
+++ b/arch/arm64/kvm/va_layout.c
@@ -10,6 +10,7 @@
#include <asm/alternative.h>
#include <asm/debug-monitors.h>
#include <asm/insn.h>
+#include <asm/kvm_asm.h>
#include <asm/kvm_mmu.h>
#include <asm/memory.h>
@@ -82,6 +83,81 @@ __init void kvm_compute_layout(void)
init_hyp_physvirt_offset();
}
+#define __load_elf_u64(s) \
+ ({ \
+ extern u64 s; \
+ u64 val; \
+ \
+ asm ("ldr %0, =%1" : "=r"(val) : "S"(&s)); \
+ val; \
+ })
I'm not sure I get the rational about the naming here. None of this
has much to do with ELF, but seems to just load a value from a
constant pool.
+
+static bool __is_within_bounds(u64 addr, char *start, char *end)
+{
+ return start <= (char*)addr && (char*)addr < end;
+}
+
+static bool __is_in_hyp_section(u64 addr)
+{
+ return __is_within_bounds(addr, __hyp_text_start, __hyp_text_end) ||
+ __is_within_bounds(addr, __hyp_rodata_start, __hyp_rodata_end)
||
+ __is_within_bounds(addr,
+ CHOOSE_NVHE_SYM(__per_cpu_start),
+ CHOOSE_NVHE_SYM(__per_cpu_end));
+}
+
+static void __fixup_hyp_rel(u64 addr)
+{
+ u64 *ptr, kern_va, hyp_va;
+
+ /* Adjust the relocation address taken from ELF for KASLR. */
+ addr += kaslr_offset();
+
+ /* Skip addresses not in any of the hyp sections. */
+ if (!__is_in_hyp_section(addr))
+ return;
+
+ /* Get the LM alias of the relocation address. */
+ ptr = (u64*)kvm_ksym_ref((void*)addr);
Why the casting? We should be perfectly fine without.
nit: we really need to change the name of this helper, it doesn't have
anything to do with symbols anymore. And actually, lm_alias() *is* the
right thing to use here (we don't relocate anything on VHE).
+
+ /*
+ * Read the value at the relocation address. It has already been
+ * relocated to the actual kernel kimg VA.
+ */
+ kern_va = (u64)kvm_ksym_ref((void*)*ptr);
Same comment.
+
+ /* Convert to hyp VA. */
+ hyp_va = __early_kern_hyp_va(kern_va);
+
+ /* Store hyp VA at the relocation address. */
+ *ptr = __early_kern_hyp_va(kern_va);
+}
+
+static void __fixup_hyp_rela(void)
+{
+ Elf64_Rela *rel;
+ size_t i, n;
+
+ rel = (Elf64_Rela*)(kimage_vaddr + __load_elf_u64(__rela_offset));
+ n = __load_elf_u64(__rela_size) / sizeof(*rel);
+
+ for (i = 0; i < n; ++i)
+ __fixup_hyp_rel(rel[i].r_offset);
+}
+
+/*
+ * The kernel relocated pointers to kernel VA. Iterate over
relocations in
+ * the hypervisor ELF sections and convert them to hyp VA. This avoids
the
+ * need to only use PC-relative addressing in hyp.
+ */
+__init void kvm_fixup_hyp_relocations(void)
+{
+ if (!IS_ENABLED(CONFIG_RELOCATABLE) || has_vhe())
What do we do if CONFIG_RELOCATABLE is not selected? As far as I can
tell,
bad things will happen...
I'm also worried that at this stage, the kernel is broken, until you
remove the other bits involved in runtime offsetting pointers.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
