Joerg Roedel
2021-May-19 13:16 UTC
[PATCH 2/6] x86/sev-es: Forward page-faults which happen during emulation
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