On Thu, Oct 31, 2019 at 09:46:23AM -0700, samitolvanen@xxxxxxxxxx wrote: > 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/ > Co-developed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > [ updated commit message, switched from x18 to x29 for the guest context ] > Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -Kees > --- > arch/arm64/kvm/hyp/entry.S | 41 +++++++++++++++++++------------------- > 1 file changed, 20 insertions(+), 21 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S > index e5cc8d66bf53..c3c2d842c609 100644 > --- a/arch/arm64/kvm/hyp/entry.S > +++ b/arch/arm64/kvm/hyp/entry.S > @@ -23,6 +23,7 @@ > .pushsection .hyp.text, "ax" > > .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 +33,8 @@ > .endm > > .macro restore_callee_saved_regs ctxt > + // We assume \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 +51,7 @@ 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 +70,28 @@ 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 +114,7 @@ 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 +123,8 @@ 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 > -- > 2.24.0.rc0.303.g954a862665-goog > -- Kees Cook
