From 71dcb8be6d29cffff3f4a4463232f38786e97797 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Tue, 27 Feb 2018 17:38:08 +0000 Subject: arm64: KVM: Allow far branches from vector slots to the main vectors So far, the branch from the vector slots to the main vectors can at most be 4GB from the main vectors (the reach of ADRP), and this distance is known at compile time. If we were to remap the slots to an unrelated VA, things would break badly. A way to achieve VA independence would be to load the absolute address of the vectors (__kvm_hyp_vector), either using a constant pool or a series of movs, followed by an indirect branch. This patches implements the latter solution, using another instance of a patching callback. Note that since we have to save a register pair on the stack, we branch to the *second* instruction in the vectors in order to compensate for it. This also results in having to adjust this balance in the invalid vector entry point. Acked-by: Catalin Marinas Signed-off-by: Marc Zyngier --- arch/arm64/include/asm/cpucaps.h | 2 +- arch/arm64/kernel/bpi.S | 21 ++++++++++++ arch/arm64/kvm/hyp/hyp-entry.S | 2 ++ arch/arm64/kvm/va_layout.c | 72 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 96 insertions(+), 1 deletion(-) (limited to 'arch/arm64') diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h index 76a43a17449a..d4cc54ed0656 100644 --- a/arch/arm64/include/asm/cpucaps.h +++ b/arch/arm64/include/asm/cpucaps.h @@ -32,7 +32,7 @@ #define ARM64_HAS_VIRT_HOST_EXTN 11 #define ARM64_WORKAROUND_CAVIUM_27456 12 #define ARM64_HAS_32BIT_EL0 13 -/* #define ARM64_UNALLOCATED_ENTRY 14 */ +#define ARM64_HARDEN_EL2_VECTORS 14 #define ARM64_MISMATCHED_CACHE_LINE_SIZE 15 #define ARM64_HAS_NO_FPSIMD 16 #define ARM64_WORKAROUND_REPEAT_TLBI 17 diff --git a/arch/arm64/kernel/bpi.S b/arch/arm64/kernel/bpi.S index ce1cfe3b24e6..dc51ef2ce98a 100644 --- a/arch/arm64/kernel/bpi.S +++ b/arch/arm64/kernel/bpi.S @@ -19,16 +19,37 @@ #include #include +#include + .macro hyp_ventry .align 7 1: .rept 27 nop .endr +/* + * The default sequence is to directly branch to the KVM vectors, + * using the computed offset. This applies for VHE as well as + * !ARM64_HARDEN_EL2_VECTORS. + * + * For ARM64_HARDEN_EL2_VECTORS configurations, this gets replaced + * with: + * + * stp x0, x1, [sp, #-16]! + * movz x0, #(addr & 0xffff) + * movk x0, #((addr >> 16) & 0xffff), lsl #16 + * movk x0, #((addr >> 32) & 0xffff), lsl #32 + * br x0 + * + * Where addr = kern_hyp_va(__kvm_hyp_vector) + vector-offset + 4. + * See kvm_patch_vector_branch for details. + */ +alternative_cb kvm_patch_vector_branch b __kvm_hyp_vector + (1b - 0b) nop nop nop nop +alternative_cb_end .endm .macro generate_vectors diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S index 8359fed89098..87dfecce82b1 100644 --- a/arch/arm64/kvm/hyp/hyp-entry.S +++ b/arch/arm64/kvm/hyp/hyp-entry.S @@ -212,6 +212,8 @@ ENDPROC(\label) .macro invalid_vect target .align 7 b \target + ldp x0, x1, [sp], #16 + b \target .endm ENTRY(__kvm_hyp_vector) diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c index 3d41a480b6a5..2deb6e9874c9 100644 --- a/arch/arm64/kvm/va_layout.c +++ b/arch/arm64/kvm/va_layout.c @@ -150,3 +150,75 @@ void __init kvm_update_va_mask(struct alt_instr *alt, updptr[i] = cpu_to_le32(insn); } } + +void kvm_patch_vector_branch(struct alt_instr *alt, + __le32 *origptr, __le32 *updptr, int nr_inst) +{ + u64 addr; + u32 insn; + + BUG_ON(nr_inst != 5); + + if (has_vhe() || !cpus_have_const_cap(ARM64_HARDEN_EL2_VECTORS)) { + WARN_ON_ONCE(cpus_have_const_cap(ARM64_HARDEN_EL2_VECTORS)); + return; + } + + if (!va_mask) + compute_layout(); + + /* + * Compute HYP VA by using the same computation as kern_hyp_va() + */ + addr = (uintptr_t)kvm_ksym_ref(__kvm_hyp_vector); + addr &= va_mask; + addr |= tag_val << tag_lsb; + + /* Use PC[10:7] to branch to the same vector in KVM */ + addr |= ((u64)origptr & GENMASK_ULL(10, 7)); + + /* + * Branch to the second instruction in the vectors in order to + * avoid the initial store on the stack (which we already + * perform in the hardening vectors). + */ + addr += AARCH64_INSN_SIZE; + + /* stp x0, x1, [sp, #-16]! */ + insn = aarch64_insn_gen_load_store_pair(AARCH64_INSN_REG_0, + AARCH64_INSN_REG_1, + AARCH64_INSN_REG_SP, + -16, + AARCH64_INSN_VARIANT_64BIT, + AARCH64_INSN_LDST_STORE_PAIR_PRE_INDEX); + *updptr++ = cpu_to_le32(insn); + + /* movz x0, #(addr & 0xffff) */ + insn = aarch64_insn_gen_movewide(AARCH64_INSN_REG_0, + (u16)addr, + 0, + AARCH64_INSN_VARIANT_64BIT, + AARCH64_INSN_MOVEWIDE_ZERO); + *updptr++ = cpu_to_le32(insn); + + /* movk x0, #((addr >> 16) & 0xffff), lsl #16 */ + insn = aarch64_insn_gen_movewide(AARCH64_INSN_REG_0, + (u16)(addr >> 16), + 16, + AARCH64_INSN_VARIANT_64BIT, + AARCH64_INSN_MOVEWIDE_KEEP); + *updptr++ = cpu_to_le32(insn); + + /* movk x0, #((addr >> 32) & 0xffff), lsl #32 */ + insn = aarch64_insn_gen_movewide(AARCH64_INSN_REG_0, + (u16)(addr >> 32), + 32, + AARCH64_INSN_VARIANT_64BIT, + AARCH64_INSN_MOVEWIDE_KEEP); + *updptr++ = cpu_to_le32(insn); + + /* br x0 */ + insn = aarch64_insn_gen_branch_reg(AARCH64_INSN_REG_0, + AARCH64_INSN_BRANCH_NOLINK); + *updptr++ = cpu_to_le32(insn); +} -- cgit v1.2.3