From af12376814a5d8d2fa1c86eaa3adacf9dee2102e Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Fri, 6 Dec 2019 14:13:39 -0800 Subject: 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: Ard Biesheuvel [Sami: updated commit message, switched from x18 to x29 for the guest context] Signed-off-by: Sami Tolvanen Reviewed-by: Kees Cook Reviewed-by: Marc Zyngier Reviewed-by: Mark Rutland Signed-off-by: Will Deacon --- arch/arm64/kvm/hyp/entry.S | 45 ++++++++++++++++++++++++--------------------- 1 file changed, 24 insertions(+), 21 deletions(-) (limited to 'arch/arm64/kvm') diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S index e5cc8d66bf53..0c6832ec52b1 100644 --- a/arch/arm64/kvm/hyp/entry.S +++ b/arch/arm64/kvm/hyp/entry.S @@ -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 -- cgit v1.2.3-59-g8ed1b