[PATCH v5 0/8] KVM: arm64: Add support for hypervisor kCFI

[PATCH v5 0/8] KVM: arm64: Add support for hypervisor kCFI

[Pierre-Clément Tosi]

CONFIG_CFI_CLANG ("kernel Control Flow Integrity") makes the compiler inject
runtime type checks before any indirect function call. On AArch64, it generates
a BRK instruction to be executed on type mismatch and encodes the indices of the
registers holding the branch target and expected type in the immediate of the
instruction. As a result, a synchronous exception gets triggered on kCFI failure
and the fault handler can retrieve the immediate (and indices) from ESR_ELx.

This feature has been supported at EL1 ("host") since it was introduced by
b26e484b8bb3 ("arm64: Add CFI error handling"), where cfi_handler() decodes
ESR_EL1, giving informative panic messages such as

  [   21.885179] CFI failure at lkdtm_indirect_call+0x2c/0x44 [lkdtm]
  (target: lkdtm_increment_int+0x0/0x1c [lkdtm]; expected type: 0x7e0c52a)
  [   21.886593] Internal error: Oops - CFI: 0 [#1] PREEMPT SMP

However, it is not supported at EL2 in nVHE (or pKVM), as CONFIG_CFI_CLANG gets
filtered out at build time, preventing the compiler from injecting the checks.

To address this,

- [1/8] fixes an existing bug where the ELR_EL2 was getting clobbered on
  synchronous exceptions, causing the wrong "PC" to be reported by
  nvhe_hyp_panic_handler() or __hyp_call_panic(). This is particularly limiting
  for kCFI, as it would mask the location of the failed type check.
- [2/8] fixes a minor C/asm ABI mismatch which would trigger a kCFI failure
- [3/8]-[7/8] prepare nVHE for CONFIG_CFI_CLANG and [8/8] enables it

Note that kCFI errors remain fatal at EL2, even when CONFIG_CFI_PERMISSIVE=y.

Changes in v5 (addressed Will's comments on v4):
  - Dropped the patch making the handlers report the kCFI target & expected type
  - Dropped the hypervisor kCFI test module
  - Dropped the patch introducing handler for EL2h sync exceptions
  - Dropped the patch renaming __guest_exit_panic
  - Made invalid_host_el2_vect branch unconditionally to hyp_panic
  - Changed SP type in __pkvm_init_switch_pgd signature to unsigned long
  - Changed which registers __pkvm_init_switch_pgd used for intermediates
  - Fixed typo in commit message about esr_brk_comment()
  - Fixed mistake in commit message about context of invalid_host_el2_vect

Pierre-Clément Tosi (8):
  KVM: arm64: Fix clobbered ELR in sync abort/SError
  KVM: arm64: Fix __pkvm_init_switch_pgd call ABI
  KVM: arm64: nVHE: Simplify invalid_host_el2_vect
  KVM: arm64: nVHE: gen-hyprel: Skip R_AARCH64_ABS32
  KVM: arm64: VHE: Mark __hyp_call_panic __noreturn
  arm64: Introduce esr_brk_comment, esr_is_cfi_brk
  KVM: arm64: Introduce print_nvhe_hyp_panic helper
  KVM: arm64: nVHE: Support CONFIG_CFI_CLANG at EL2

 arch/arm64/include/asm/esr.h            | 11 +++++++++
 arch/arm64/include/asm/kvm_hyp.h        |  4 ++--
 arch/arm64/kernel/asm-offsets.c         |  1 +
 arch/arm64/kernel/debug-monitors.c      |  4 +---
 arch/arm64/kernel/traps.c               |  8 +++----
 arch/arm64/kvm/handle_exit.c            | 24 +++++++++++++++-----
 arch/arm64/kvm/hyp/entry.S              |  8 +++++++
 arch/arm64/kvm/hyp/include/hyp/switch.h |  5 +++--
 arch/arm64/kvm/hyp/nvhe/Makefile        |  6 ++---
 arch/arm64/kvm/hyp/nvhe/gen-hyprel.c    |  6 +++++
 arch/arm64/kvm/hyp/nvhe/host.S          |  6 -----
 arch/arm64/kvm/hyp/nvhe/hyp-init.S      | 30 +++++++++++++++----------
 arch/arm64/kvm/hyp/nvhe/setup.c         |  4 ++--
 arch/arm64/kvm/hyp/vhe/switch.c         |  3 +--
 14 files changed, 78 insertions(+), 42 deletions(-)

-- 
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[PATCH v5 1/8] KVM: arm64: Fix clobbered ELR in sync abort/SError

[Pierre-Clément Tosi]

When the hypervisor receives a SError or synchronous exception (EL2h)
while running with the __kvm_hyp_vector and if ELR_EL2 doesn't point to
an extable entry, it panics indirectly by overwriting ELR with the
address of a panic handler in order for the asm routine it returns to to
ERET into the handler.

However, this clobbers ELR_EL2 for the handler itself. As a result,
hyp_panic(), when retrieving what it believes to be the PC where the
exception happened, actually ends up reading the address of the panic
handler that called it! This results in an erroneous and confusing panic
message where the source of any synchronous exception (e.g. BUG() or
kCFI) appears to be __guest_exit_panic, making it hard to locate the
actual BRK instruction.

Therefore, store the original ELR_EL2 in the per-CPU kvm_hyp_ctxt and
point the sysreg to a routine that first restores it to its previous
value before running __guest_exit_panic.

Fixes: 7db21530479f ("KVM: arm64: Restore hyp when panicking in guest context")
Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
Acked-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/asm-offsets.c         | 1 +
 arch/arm64/kvm/hyp/entry.S              | 8 ++++++++
 arch/arm64/kvm/hyp/include/hyp/switch.h | 5 +++--
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 81496083c041..27de1dddb0ab 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -128,6 +128,7 @@ int main(void)
   DEFINE(VCPU_FAULT_DISR,	offsetof(struct kvm_vcpu, arch.fault.disr_el1));
   DEFINE(VCPU_HCR_EL2,		offsetof(struct kvm_vcpu, arch.hcr_el2));
   DEFINE(CPU_USER_PT_REGS,	offsetof(struct kvm_cpu_context, regs));
+  DEFINE(CPU_ELR_EL2,		offsetof(struct kvm_cpu_context, sys_regs[ELR_EL2]));
   DEFINE(CPU_RGSR_EL1,		offsetof(struct kvm_cpu_context, sys_regs[RGSR_EL1]));
   DEFINE(CPU_GCR_EL1,		offsetof(struct kvm_cpu_context, sys_regs[GCR_EL1]));
   DEFINE(CPU_APIAKEYLO_EL1,	offsetof(struct kvm_cpu_context, sys_regs[APIAKEYLO_EL1]));
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index f3aa7738b477..4433a234aa9b 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -83,6 +83,14 @@ alternative_else_nop_endif
 	eret
 	sb
 
+SYM_INNER_LABEL(__guest_exit_restore_elr_and_panic, SYM_L_GLOBAL)
+	// x2-x29,lr: vcpu regs
+	// vcpu x0-x1 on the stack
+
+	adr_this_cpu x0, kvm_hyp_ctxt, x1
+	ldr	x0, [x0, #CPU_ELR_EL2]
+	msr	elr_el2, x0
+
 SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)
 	// x2-x29,lr: vcpu regs
 	// vcpu x0-x1 on the stack
diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index a92566f36022..ed9a63f1f7bf 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -689,7 +689,7 @@ static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
 
 static inline void __kvm_unexpected_el2_exception(void)
 {
-	extern char __guest_exit_panic[];
+	extern char __guest_exit_restore_elr_and_panic[];
 	unsigned long addr, fixup;
 	struct kvm_exception_table_entry *entry, *end;
 	unsigned long elr_el2 = read_sysreg(elr_el2);
@@ -711,7 +711,8 @@ static inline void __kvm_unexpected_el2_exception(void)
 	}
 
 	/* Trigger a panic after restoring the hyp context. */
-	write_sysreg(__guest_exit_panic, elr_el2);
+	this_cpu_ptr(&kvm_hyp_ctxt)->sys_regs[ELR_EL2] = elr_el2;
+	write_sysreg(__guest_exit_restore_elr_and_panic, elr_el2);
 }
 
 #endif /* __ARM64_KVM_HYP_SWITCH_H__ */
-- 
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[PATCH v5 2/8] KVM: arm64: Fix __pkvm_init_switch_pgd call ABI

[Pierre-Clément Tosi]

Fix the mismatch between the (incorrect) C signature, C call site, and
asm implementation by aligning all three on an API passing the
parameters (pgd and SP) separately, instead of as a bundled struct.

Remove the now unnecessary memory accesses while the MMU is off from the
asm, which simplifies the C caller (as it does not need to convert a VA
struct pointer to PA) and makes the code slightly more robust by
offsetting the struct fields from C and properly expressing the call to
the C compiler (e.g. type checker and kCFI).

Fixes: f320bc742bc2 ("KVM: arm64: Prepare the creation of s1 mappings at EL2")
Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
---
 arch/arm64/include/asm/kvm_hyp.h   |  4 ++--
 arch/arm64/kvm/hyp/nvhe/hyp-init.S | 24 +++++++++++++-----------
 arch/arm64/kvm/hyp/nvhe/setup.c    |  4 ++--
 3 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
index 3e80464f8953..181e10e2575b 100644
--- a/arch/arm64/include/asm/kvm_hyp.h
+++ b/arch/arm64/include/asm/kvm_hyp.h
@@ -123,8 +123,8 @@ void __noreturn __hyp_do_panic(struct kvm_cpu_context *host_ctxt, u64 spsr,
 #endif
 
 #ifdef __KVM_NVHE_HYPERVISOR__
-void __pkvm_init_switch_pgd(phys_addr_t phys, unsigned long size,
-			    phys_addr_t pgd, void *sp, void *cont_fn);
+void __pkvm_init_switch_pgd(phys_addr_t pgd, unsigned long sp,
+		void (*fn)(void));
 int __pkvm_init(phys_addr_t phys, unsigned long size, unsigned long nr_cpus,
 		unsigned long *per_cpu_base, u32 hyp_va_bits);
 void __noreturn __host_enter(struct kvm_cpu_context *host_ctxt);
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
index 2994878d68ea..3a2836a52e85 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
@@ -265,33 +265,35 @@ alternative_else_nop_endif
 
 SYM_CODE_END(__kvm_handle_stub_hvc)
 
+/*
+ * void __pkvm_init_switch_pgd(phys_addr_t pgd, unsigned long sp,
+ *                             void (*fn)(void));
+ */
 SYM_FUNC_START(__pkvm_init_switch_pgd)
 	/* Turn the MMU off */
 	pre_disable_mmu_workaround
-	mrs	x2, sctlr_el2
-	bic	x3, x2, #SCTLR_ELx_M
-	msr	sctlr_el2, x3
+	mrs	x3, sctlr_el2
+	bic	x4, x3, #SCTLR_ELx_M
+	msr	sctlr_el2, x4
 	isb
 
 	tlbi	alle2
 
 	/* Install the new pgtables */
-	ldr	x3, [x0, #NVHE_INIT_PGD_PA]
-	phys_to_ttbr x4, x3
+	phys_to_ttbr x5, x0
 alternative_if ARM64_HAS_CNP
-	orr	x4, x4, #TTBR_CNP_BIT
+	orr	x5, x5, #TTBR_CNP_BIT
 alternative_else_nop_endif
-	msr	ttbr0_el2, x4
+	msr	ttbr0_el2, x5
 
 	/* Set the new stack pointer */
-	ldr	x0, [x0, #NVHE_INIT_STACK_HYP_VA]
-	mov	sp, x0
+	mov	sp, x1
 
 	/* And turn the MMU back on! */
 	dsb	nsh
 	isb
-	set_sctlr_el2	x2
-	ret	x1
+	set_sctlr_el2	x3
+	ret	x2
 SYM_FUNC_END(__pkvm_init_switch_pgd)
 
 	.popsection
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index 859f22f754d3..598f688b678f 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -316,7 +316,7 @@ int __pkvm_init(phys_addr_t phys, unsigned long size, unsigned long nr_cpus,
 {
 	struct kvm_nvhe_init_params *params;
 	void *virt = hyp_phys_to_virt(phys);
-	void (*fn)(phys_addr_t params_pa, void *finalize_fn_va);
+	typeof(__pkvm_init_switch_pgd) *fn;
 	int ret;
 
 	BUG_ON(kvm_check_pvm_sysreg_table());
@@ -340,7 +340,7 @@ int __pkvm_init(phys_addr_t phys, unsigned long size, unsigned long nr_cpus,
 	/* Jump in the idmap page to switch to the new page-tables */
 	params = this_cpu_ptr(&kvm_init_params);
 	fn = (typeof(fn))__hyp_pa(__pkvm_init_switch_pgd);
-	fn(__hyp_pa(params), __pkvm_init_finalise);
+	fn(params->pgd_pa, params->stack_hyp_va, __pkvm_init_finalise);
 
 	unreachable();
 }
-- 
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[PATCH v5 3/8] KVM: arm64: nVHE: Simplify invalid_host_el2_vect

[Pierre-Clément Tosi]

The invalid_host_el2_vect macro is used by EL2{t,h} handlers in nVHE
*host* context, which should never run with a guest context loaded.
Therefore, remove the superfluous vCPU context check and branch
unconditionally to hyp_panic.

Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
---
 arch/arm64/kvm/hyp/nvhe/host.S | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
index 135cfb294ee5..3d610fc51f4d 100644
--- a/arch/arm64/kvm/hyp/nvhe/host.S
+++ b/arch/arm64/kvm/hyp/nvhe/host.S
@@ -197,12 +197,6 @@ SYM_FUNC_END(__host_hvc)
 	sub	x0, sp, x0			// x0'' = sp' - x0' = (sp + x0) - sp = x0
 	sub	sp, sp, x0			// sp'' = sp' - x0 = (sp + x0) - x0 = sp
 
-	/* If a guest is loaded, panic out of it. */
-	stp	x0, x1, [sp, #-16]!
-	get_loaded_vcpu x0, x1
-	cbnz	x0, __guest_exit_panic
-	add	sp, sp, #16
-
 	/*
 	 * The panic may not be clean if the exception is taken before the host
 	 * context has been saved by __host_exit or after the hyp context has
-- 
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[PATCH v5 4/8] KVM: arm64: nVHE: gen-hyprel: Skip R_AARCH64_ABS32

[Pierre-Clément Tosi]

Ignore R_AARCH64_ABS32 relocations, instead of panicking, when emitting
the relocation table of the hypervisor. The toolchain might produce them
when generating function calls with kCFI to represent the 32-bit type ID
which can then be resolved across compilation units at link time.  These
are NOT actual 32-bit addresses and are therefore not needed in the
final (runtime) relocation table (which is unlikely to use 32-bit
absolute addresses for arm64 anyway).

Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
Acked-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kvm/hyp/nvhe/gen-hyprel.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/gen-hyprel.c b/arch/arm64/kvm/hyp/nvhe/gen-hyprel.c
index 6bc88a756cb7..b63f4e1c1033 100644
--- a/arch/arm64/kvm/hyp/nvhe/gen-hyprel.c
+++ b/arch/arm64/kvm/hyp/nvhe/gen-hyprel.c
@@ -50,6 +50,9 @@
 #ifndef R_AARCH64_ABS64
 #define R_AARCH64_ABS64			257
 #endif
+#ifndef R_AARCH64_ABS32
+#define R_AARCH64_ABS32			258
+#endif
 #ifndef R_AARCH64_PREL64
 #define R_AARCH64_PREL64		260
 #endif
@@ -383,6 +386,9 @@ static void emit_rela_section(Elf64_Shdr *sh_rela)
 		case R_AARCH64_ABS64:
 			emit_rela_abs64(rela, sh_orig_name);
 			break;
+		/* Allow 32-bit absolute relocation, for kCFI type hashes. */
+		case R_AARCH64_ABS32:
+			break;
 		/* Allow position-relative data relocations. */
 		case R_AARCH64_PREL64:
 		case R_AARCH64_PREL32:
-- 
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[PATCH v5 5/8] KVM: arm64: VHE: Mark __hyp_call_panic __noreturn

[Pierre-Clément Tosi]

Given that the sole purpose of __hyp_call_panic() is to call panic(), a
__noreturn function, give it the __noreturn attribute, removing the need
for its caller to use unreachable().

Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
Acked-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kvm/hyp/vhe/switch.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index d7af5f46f22a..0550b9f6317f 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -384,7 +384,7 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
 	return ret;
 }
 
-static void __hyp_call_panic(u64 spsr, u64 elr, u64 par)
+static void __noreturn __hyp_call_panic(u64 spsr, u64 elr, u64 par)
 {
 	struct kvm_cpu_context *host_ctxt;
 	struct kvm_vcpu *vcpu;
@@ -409,7 +409,6 @@ void __noreturn hyp_panic(void)
 	u64 par = read_sysreg_par();
 
 	__hyp_call_panic(spsr, elr, par);
-	unreachable();
 }
 
 asmlinkage void kvm_unexpected_el2_exception(void)
-- 
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[PATCH v5 6/8] arm64: Introduce esr_brk_comment, esr_is_cfi_brk

[Pierre-Clément Tosi]

As it is already used in two places, move esr_comment() to a header for
re-use, with a clearer name.

Introduce esr_is_cfi_brk() to detect kCFI BRK syndromes, currently used
by early_brk64() but soon to also be used by hypervisor code.

Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
Acked-by: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/esr.h       | 11 +++++++++++
 arch/arm64/kernel/debug-monitors.c |  4 +---
 arch/arm64/kernel/traps.c          |  8 +++-----
 arch/arm64/kvm/handle_exit.c       |  2 +-
 4 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index 7abf09df7033..77569d207ecf 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -379,6 +379,11 @@
 #ifndef __ASSEMBLY__
 #include <asm/types.h>
 
+static inline unsigned long esr_brk_comment(unsigned long esr)
+{
+	return esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
+}
+
 static inline bool esr_is_data_abort(unsigned long esr)
 {
 	const unsigned long ec = ESR_ELx_EC(esr);
@@ -386,6 +391,12 @@ static inline bool esr_is_data_abort(unsigned long esr)
 	return ec == ESR_ELx_EC_DABT_LOW || ec == ESR_ELx_EC_DABT_CUR;
 }
 
+static inline bool esr_is_cfi_brk(unsigned long esr)
+{
+	return ESR_ELx_EC(esr) == ESR_ELx_EC_BRK64 &&
+	       (esr_brk_comment(esr) & ~CFI_BRK_IMM_MASK) == CFI_BRK_IMM_BASE;
+}
+
 static inline bool esr_fsc_is_translation_fault(unsigned long esr)
 {
 	/* Translation fault, level -1 */
diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index 64f2ecbdfe5c..024a7b245056 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -312,9 +312,7 @@ static int call_break_hook(struct pt_regs *regs, unsigned long esr)
 	 * entirely not preemptible, and we can use rcu list safely here.
 	 */
 	list_for_each_entry_rcu(hook, list, node) {
-		unsigned long comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
-
-		if ((comment & ~hook->mask) == hook->imm)
+		if ((esr_brk_comment(esr) & ~hook->mask) == hook->imm)
 			fn = hook->fn;
 	}
 
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 215e6d7f2df8..9e22683aa921 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -1105,8 +1105,6 @@ static struct break_hook ubsan_break_hook = {
 };
 #endif
 
-#define esr_comment(esr) ((esr) & ESR_ELx_BRK64_ISS_COMMENT_MASK)
-
 /*
  * Initial handler for AArch64 BRK exceptions
  * This handler only used until debug_traps_init().
@@ -1115,15 +1113,15 @@ int __init early_brk64(unsigned long addr, unsigned long esr,
 		struct pt_regs *regs)
 {
 #ifdef CONFIG_CFI_CLANG
-	if ((esr_comment(esr) & ~CFI_BRK_IMM_MASK) == CFI_BRK_IMM_BASE)
+	if (esr_is_cfi_brk(esr))
 		return cfi_handler(regs, esr) != DBG_HOOK_HANDLED;
 #endif
 #ifdef CONFIG_KASAN_SW_TAGS
-	if ((esr_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
+	if ((esr_brk_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
 		return kasan_handler(regs, esr) != DBG_HOOK_HANDLED;
 #endif
 #ifdef CONFIG_UBSAN_TRAP
-	if ((esr_comment(esr) & ~UBSAN_BRK_MASK) == UBSAN_BRK_IMM)
+	if ((esr_brk_comment(esr) & ~UBSAN_BRK_MASK) == UBSAN_BRK_IMM)
 		return ubsan_handler(regs, esr) != DBG_HOOK_HANDLED;
 #endif
 	return bug_handler(regs, esr) != DBG_HOOK_HANDLED;
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index b037f0a0e27e..d41447193e13 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -423,7 +423,7 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
 	if (mode != PSR_MODE_EL2t && mode != PSR_MODE_EL2h) {
 		kvm_err("Invalid host exception to nVHE hyp!\n");
 	} else if (ESR_ELx_EC(esr) == ESR_ELx_EC_BRK64 &&
-		   (esr & ESR_ELx_BRK64_ISS_COMMENT_MASK) == BUG_BRK_IMM) {
+		   esr_brk_comment(esr) == BUG_BRK_IMM) {
 		const char *file = NULL;
 		unsigned int line = 0;
 
-- 
2.45.2.505.gda0bf45e8d-goog


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[PATCH v5 7/8] KVM: arm64: Introduce print_nvhe_hyp_panic helper

[Pierre-Clément Tosi]

Add a helper to display a panic banner soon to also be used for kCFI
failures, to ensure that we remain consistent.

Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
Acked-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kvm/handle_exit.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index d41447193e13..b3d6657a259d 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -411,6 +411,12 @@ void handle_exit_early(struct kvm_vcpu *vcpu, int exception_index)
 		kvm_handle_guest_serror(vcpu, kvm_vcpu_get_esr(vcpu));
 }
 
+static void print_nvhe_hyp_panic(const char *name, u64 panic_addr)
+{
+	kvm_err("nVHE hyp %s at: [<%016llx>] %pB!\n", name, panic_addr,
+		(void *)(panic_addr + kaslr_offset()));
+}
+
 void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
 					      u64 elr_virt, u64 elr_phys,
 					      u64 par, uintptr_t vcpu,
@@ -439,11 +445,9 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
 		if (file)
 			kvm_err("nVHE hyp BUG at: %s:%u!\n", file, line);
 		else
-			kvm_err("nVHE hyp BUG at: [<%016llx>] %pB!\n", panic_addr,
-					(void *)(panic_addr + kaslr_offset()));
+			print_nvhe_hyp_panic("BUG", panic_addr);
 	} else {
-		kvm_err("nVHE hyp panic at: [<%016llx>] %pB!\n", panic_addr,
-				(void *)(panic_addr + kaslr_offset()));
+		print_nvhe_hyp_panic("panic", panic_addr);
 	}
 
 	/* Dump the nVHE hypervisor backtrace */
-- 
2.45.2.505.gda0bf45e8d-goog


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[PATCH v5 8/8] KVM: arm64: nVHE: Support CONFIG_CFI_CLANG at EL2

[Pierre-Clément Tosi]

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@google.com>
Acked-by: Will Deacon <will@kernel.org>
---
 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 3a2836a52e85..07120b37da35 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>
@@ -268,8 +269,11 @@ SYM_CODE_END(__kvm_handle_stub_hvc)
 /*
  * void __pkvm_init_switch_pgd(phys_addr_t pgd, unsigned long 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	x3, sctlr_el2
-- 
2.45.2.505.gda0bf45e8d-goog


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Re: [PATCH v5 3/8] KVM: arm64: nVHE: Simplify invalid_host_el2_vect

[Will Deacon]

On Mon, Jun 10, 2024 at 07:32:32AM +0100, Pierre-Clément Tosi wrote:
> The invalid_host_el2_vect macro is used by EL2{t,h} handlers in nVHE
> *host* context, which should never run with a guest context loaded.
> Therefore, remove the superfluous vCPU context check and branch
> unconditionally to hyp_panic.
> 
> Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/host.S | 6 ------
>  1 file changed, 6 deletions(-)

Acked-by: Will Deacon <will@kernel.org>

Will

Re: [PATCH v5 2/8] KVM: arm64: Fix __pkvm_init_switch_pgd call ABI

[Will Deacon]

On Mon, Jun 10, 2024 at 07:32:31AM +0100, Pierre-Clément Tosi wrote:
> Fix the mismatch between the (incorrect) C signature, C call site, and
> asm implementation by aligning all three on an API passing the
> parameters (pgd and SP) separately, instead of as a bundled struct.
> 
> Remove the now unnecessary memory accesses while the MMU is off from the
> asm, which simplifies the C caller (as it does not need to convert a VA
> struct pointer to PA) and makes the code slightly more robust by
> offsetting the struct fields from C and properly expressing the call to
> the C compiler (e.g. type checker and kCFI).
> 
> Fixes: f320bc742bc2 ("KVM: arm64: Prepare the creation of s1 mappings at EL2")
> Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
> ---
>  arch/arm64/include/asm/kvm_hyp.h   |  4 ++--
>  arch/arm64/kvm/hyp/nvhe/hyp-init.S | 24 +++++++++++++-----------
>  arch/arm64/kvm/hyp/nvhe/setup.c    |  4 ++--
>  3 files changed, 17 insertions(+), 15 deletions(-)

Acked-by: Will Deacon <will@kernel.org>

Will

Re: [PATCH v5 0/8] KVM: arm64: Add support for hypervisor kCFI

[Oliver Upton]

On Mon, 10 Jun 2024 07:32:29 +0100, Pierre-Clément Tosi wrote:
> CONFIG_CFI_CLANG ("kernel Control Flow Integrity") makes the compiler inject
> runtime type checks before any indirect function call. On AArch64, it generates
> a BRK instruction to be executed on type mismatch and encodes the indices of the
> registers holding the branch target and expected type in the immediate of the
> instruction. As a result, a synchronous exception gets triggered on kCFI failure
> and the fault handler can retrieve the immediate (and indices) from ESR_ELx.
> 
> [...]

Applied to kvmarm/next, thanks!

[1/8] KVM: arm64: Fix clobbered ELR in sync abort/SError
      https://git.kernel.org/kvmarm/kvmarm/c/a8f0655887cc
[2/8] KVM: arm64: Fix __pkvm_init_switch_pgd call ABI
      https://git.kernel.org/kvmarm/kvmarm/c/ea9d7c83d14e
[3/8] KVM: arm64: nVHE: Simplify invalid_host_el2_vect
      https://git.kernel.org/kvmarm/kvmarm/c/6e3b773ed6bc
[4/8] KVM: arm64: nVHE: gen-hyprel: Skip R_AARCH64_ABS32
      https://git.kernel.org/kvmarm/kvmarm/c/4ab3f9dd561b
[5/8] KVM: arm64: VHE: Mark __hyp_call_panic __noreturn
      https://git.kernel.org/kvmarm/kvmarm/c/3c6eb6487693
[6/8] arm64: Introduce esr_brk_comment, esr_is_cfi_brk
      https://git.kernel.org/kvmarm/kvmarm/c/7a928b32f1de
[7/8] KVM: arm64: Introduce print_nvhe_hyp_panic helper
      https://git.kernel.org/kvmarm/kvmarm/c/8f3873a39529
[8/8] KVM: arm64: nVHE: Support CONFIG_CFI_CLANG at EL2
      https://git.kernel.org/kvmarm/kvmarm/c/eca4ba5b6dff

--
Best,
Oliver