The compiler implements kCFI by adding type information (u32) above
every function that might be indirectly called and, whenever a function
pointer is called, injects a read-and-compare of that u32 against the
value corresponding to the expected type. In case of a mismatch, a BRK
instruction gets executed. When the hypervisor triggers such an
exception in nVHE, it panics and triggers and exception return to EL1.
Therefore, teach nvhe_hyp_panic_handler() to detect kCFI errors from the
ESR and report them. If necessary, remind the user that EL2 kCFI is not
affected by CONFIG_CFI_PERMISSIVE.
Pass $(CC_FLAGS_CFI) to the compiler when building the nVHE hyp code.
Use SYM_TYPED_FUNC_START() for __pkvm_init_switch_pgd, as nVHE can't
call it directly and must use a PA function pointer from C (because it
is part of the idmap page), which would trigger a kCFI failure if the
type ID wasn't present.
Signed-off-by: Pierre-Clément Tosi <ptosi@xxxxxxxxxx>
---
arch/arm64/kvm/handle_exit.c | 10 ++++++++++
arch/arm64/kvm/hyp/nvhe/Makefile | 6 +++---
arch/arm64/kvm/hyp/nvhe/hyp-init.S | 6 +++++-
3 files changed, 18 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index b3d6657a259d..69b08ac7322d 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -417,6 +417,14 @@ static void print_nvhe_hyp_panic(const char *name, u64 panic_addr)
(void *)(panic_addr + kaslr_offset()));
}
+static void kvm_nvhe_report_cfi_failure(u64 panic_addr)
+{
+ print_nvhe_hyp_panic("CFI failure", panic_addr);
+
+ if (IS_ENABLED(CONFIG_CFI_PERMISSIVE))
+ kvm_err(" (CONFIG_CFI_PERMISSIVE ignored for hyp failures)\n");
+}
+
void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
u64 elr_virt, u64 elr_phys,
u64 par, uintptr_t vcpu,
@@ -446,6 +454,8 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
kvm_err("nVHE hyp BUG at: %s:%u!\n", file, line);
else
print_nvhe_hyp_panic("BUG", panic_addr);
+ } else if (IS_ENABLED(CONFIG_CFI_CLANG) && esr_is_cfi_brk(esr)) {
+ kvm_nvhe_report_cfi_failure(panic_addr);
} else {
print_nvhe_hyp_panic("panic", panic_addr);
}
diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index 50fa0ffb6b7e..782b34b004be 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -89,9 +89,9 @@ quiet_cmd_hyprel = HYPREL $@
quiet_cmd_hypcopy = HYPCOPY $@
cmd_hypcopy = $(OBJCOPY) --prefix-symbols=__kvm_nvhe_ $< $@
-# Remove ftrace, Shadow Call Stack, and CFI CFLAGS.
-# This is equivalent to the 'notrace', '__noscs', and '__nocfi' annotations.
-KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS) $(CC_FLAGS_CFI), $(KBUILD_CFLAGS))
+# Remove ftrace and Shadow Call Stack CFLAGS.
+# This is equivalent to the 'notrace' and '__noscs' annotations.
+KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
# Starting from 13.0.0 llvm emits SHT_REL section '.llvm.call-graph-profile'
# when profile optimization is applied. gen-hyprel does not support SHT_REL and
# causes a build failure. Remove profile optimization flags.
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
index d859c4de06b6..b1c8977e2812 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
@@ -5,6 +5,7 @@
*/
#include <linux/arm-smccc.h>
+#include <linux/cfi_types.h>
#include <linux/linkage.h>
#include <asm/alternative.h>
@@ -267,8 +268,11 @@ SYM_CODE_END(__kvm_handle_stub_hvc)
/*
* void __pkvm_init_switch_pgd(phys_addr_t pgd, void *sp, void (*fn)(void));
+ *
+ * SYM_TYPED_FUNC_START() allows C to call this ID-mapped function indirectly
+ * using a physical pointer without triggering a kCFI failure.
*/
-SYM_FUNC_START(__pkvm_init_switch_pgd)
+SYM_TYPED_FUNC_START(__pkvm_init_switch_pgd)
/* Turn the MMU off */
pre_disable_mmu_workaround
mrs x9, sctlr_el2
--
2.45.1.288.g0e0cd299f1-goog
