Re: [PATCH 2/6] x86/sev-es: Forward page-faults which happen during emulation
flat view
From: Joerg Roedel <joro@8bytes.org>
Date: 2021-05-19 13:16:46
Also in:
kvm, linux-coco, lkml, stable
Hi Sean, On Wed, May 12, 2021 at 05:31:03PM +0000, Sean Christopherson wrote:
This got me looking at the flows that "inject" #PF, and I'm pretty sure there
are bugs in __vc_decode_user_insn() + insn_get_effective_ip().
Problem #1: __vc_decode_user_insn() assumes a #PF if insn_fetch_from_user_inatomic()
fails, but the majority of failure cases in insn_get_seg_base() are #GPs, not #PF.
res = insn_fetch_from_user_inatomic(ctxt->regs, buffer);
if (!res) {
ctxt->fi.vector = X86_TRAP_PF;
ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
ctxt->fi.cr2 = ctxt->regs->ip;
return ES_EXCEPTION;
}
Problem #2: Using '0' as an error code means a legitimate effective IP of '0'
will be misinterpreted as a failure. Practically speaking, I highly doubt anyone
will ever actually run code at address 0, but it's technically possible. The
most robust approach would be to pass a pointer to @ip and return an actual error
code. Using a non-canonical magic value might also work, but that could run afoul
of future shenanigans like LAM.
ip = insn_get_effective_ip(regs);
if (!ip)
return 0;Your observations are all correct. I put some changes onto this patch-set to fix these problems. Regards, Joerg _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization