Commit af123768 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Will Deacon
Browse files

arm64: kvm: stop treating register x18 as caller save 

In preparation of reserving x18, stop treating it as caller save in
the KVM guest entry/exit code. Currently, the code assumes there is
no need to preserve it for the host, given that it would have been
assumed clobbered anyway by the function call to __guest_enter().
Instead, preserve its value and restore it upon return.

Link: https://patchwork.kernel.org/patch/9836891/


Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
[Sami: updated commit message, switched from x18 to x29 for the guest context]
Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarMarc Zyngier <maz@kernel.org>
Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 7f153ccb

arch/arm64/kvm/hyp/entry.S

+24 −21
Original line number Diff line number Diff line
@@ -22,7 +22,12 @@ 
	.text

	.pushsection	.hyp.text, "ax"



/*

 * We treat x18 as callee-saved as the host may use it as a platform

 * register (e.g. for shadow call stack).

 */

.macro save_callee_saved_regs ctxt

	str	x18,      [\ctxt, #CPU_XREG_OFFSET(18)]

	stp	x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)]

	stp	x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)]

	stp	x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)]
@@ -32,6 +37,8 @@ 
.endm



.macro restore_callee_saved_regs ctxt

	// We require \ctxt is not x18-x28

	ldr	x18,      [\ctxt, #CPU_XREG_OFFSET(18)]

	ldp	x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)]

	ldp	x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)]

	ldp	x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)]
@@ -48,7 +55,7 @@ ENTRY(__guest_enter) 
	// x0: vcpu

	// x1: host context

	// x2-x17: clobbered by macros

	// x18: guest context

	// x29: guest context



	// Store the host regs

	save_callee_saved_regs x1
@@ -67,31 +74,28 @@ alternative_else_nop_endif 
	ret



1:

	add	x18, x0, #VCPU_CONTEXT

	add	x29, x0, #VCPU_CONTEXT



	// Macro ptrauth_switch_to_guest format:

	// 	ptrauth_switch_to_guest(guest cxt, tmp1, tmp2, tmp3)

	// The below macro to restore guest keys is not implemented in C code

	// as it may cause Pointer Authentication key signing mismatch errors

	// when this feature is enabled for kernel code.

	ptrauth_switch_to_guest x18, x0, x1, x2

	ptrauth_switch_to_guest x29, x0, x1, x2



	// Restore guest regs x0-x17

	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]

	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]

	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]

	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]

	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]

	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]

	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]

	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]

	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]



	// Restore guest regs x19-x29, lr

	restore_callee_saved_regs x18



	// Restore guest reg x18

	ldr	x18,      [x18, #CPU_XREG_OFFSET(18)]

	ldp	x0, x1,   [x29, #CPU_XREG_OFFSET(0)]

	ldp	x2, x3,   [x29, #CPU_XREG_OFFSET(2)]

	ldp	x4, x5,   [x29, #CPU_XREG_OFFSET(4)]

	ldp	x6, x7,   [x29, #CPU_XREG_OFFSET(6)]

	ldp	x8, x9,   [x29, #CPU_XREG_OFFSET(8)]

	ldp	x10, x11, [x29, #CPU_XREG_OFFSET(10)]

	ldp	x12, x13, [x29, #CPU_XREG_OFFSET(12)]

	ldp	x14, x15, [x29, #CPU_XREG_OFFSET(14)]

	ldp	x16, x17, [x29, #CPU_XREG_OFFSET(16)]



	// Restore guest regs x18-x29, lr

	restore_callee_saved_regs x29



	// Do not touch any register after this!

	eret
@@ -114,7 +118,7 @@ ENTRY(__guest_exit) 
	// Retrieve the guest regs x0-x1 from the stack

	ldp	x2, x3, [sp], #16	// x0, x1



	// Store the guest regs x0-x1 and x4-x18

	// Store the guest regs x0-x1 and x4-x17

	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]

	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]

	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
@@ -123,9 +127,8 @@ ENTRY(__guest_exit) 
	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]

	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]

	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]

	str	x18,      [x1, #CPU_XREG_OFFSET(18)]



	// Store the guest regs x19-x29, lr

	// Store the guest regs x18-x29, lr

	save_callee_saved_regs x1



	get_host_ctxt	x2, x3

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