Commit 71dcb8be authored by Marc Zyngier's avatar Marc Zyngier
Browse files

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: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
parent f0445dfa
......@@ -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
......
......@@ -19,16 +19,37 @@
#include <linux/linkage.h>
#include <linux/arm-smccc.h>
#include <asm/alternative.h>
.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
......
......@@ -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)
......
......@@ -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);
}
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