Hi Marc,
On 01/03/18 15:55, Marc Zyngier wrote:
> 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.
> diff --git a/arch/arm64/kernel/bpi.S b/arch/arm64/kernel/bpi.S
> index e000cb390618..e8d997788ad0 100644
> --- a/arch/arm64/kernel/bpi.S
> +++ b/arch/arm64/kernel/bpi.S
> @@ -19,6 +19,9 @@
> #include <linux/linkage.h>
> #include <linux/arm-smccc.h>
>
> +#include <asm/alternative.h>
> +#include <asm/kvm_mmu.h>
> +
> .macro hyp_ventry offset
> .align 7
> .rept 29
> @@ -64,9 +67,15 @@ ENTRY(__bp_harden_hyp_vecs_start)
> .endr
>
> __kvm_enter_vectors:
> +alternative_cb kvm_patch_vector_branch
> + movz x1, #0
> + movk x1, #0, lsl #16
> + movk x1, #0, lsl #32
> + movk x1, #0, lsl #48
> +alternative_cb_end
>
> - adr_l x1, __kvm_hyp_vector
> add x0, x1, x0
> + kern_hyp_va x0
Can't you patch the kern_hyp_va address into the movk block directly?
Obviously you can't call kern_hyp_va, but you could generate the layout and have
some slow __kern_hyp_va() to generate the value. This would avoid generating a
value, to then throw half of it away and patch something else in.
Does this code run for VHE systems too? (it not, is the x<<48 movk needed?)
Thanks,
James
> br x0
> ENTRY(__bp_harden_hyp_vecs_end)
>
> diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c
> index a73e47804972..7ef3d920c8d4 100644
> --- a/arch/arm64/kvm/va_layout.c
> +++ b/arch/arm64/kvm/va_layout.c
> @@ -152,3 +152,30 @@ 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)
> +{
> + enum aarch64_insn_movewide_type type;
> + u64 addr;
> + u32 oinsn, rd;
> + int s;
> +
> + BUG_ON(nr_inst != 4);
> +
> + addr = (uintptr_t)kvm_ksym_ref(__kvm_hyp_vector);
> + oinsn = le32_to_cpu(origptr[0]);
> + rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD, oinsn);
> +
> + type = AARCH64_INSN_MOVEWIDE_ZERO;
> + for (s = 0; nr_inst--; s += 16) {
> + u32 insn = aarch64_insn_gen_movewide(rd,
> + (u16)(addr >> s),
> + s,
> + AARCH64_INSN_VARIANT_64BIT,
> + type);
> + *updptr++ = cpu_to_le32(insn);
> + type = AARCH64_INSN_MOVEWIDE_KEEP;
> + }
> +
> +}
>
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