[tip: x86/sev] x86/sev: Propagate #GP if getting linear instruction address failed

tip-bot2 for Joerg Roedel
2021-06-15T10:52:13Z

The following commit has been merged into the x86/sev branch of tip:

Commit-ID: 07570cef5e5c3fcec40f82a9075abb4c1da63319
Gitweb: https://git.kernel.org/tip/07570cef5e5c3fcec40f82a9075abb4c1da63319
Author: Joerg Roedel <jroedel@suse.de>
AuthorDate: Mon, 14 Jun 2021 15:53:27 +02:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Tue, 15 Jun 2021 11:55:26 +02:00

x86/sev: Propagate #GP if getting linear instruction address failed

When an instruction is fetched from user-space, segmentation needs to
be taken into account. This means that getting the linear address of an
instruction can fail. Hardware would raise a #GP exception in that case,
but the #VC exception handler would emulate it as a page-fault.

The insn_fetch_from_user*() functions now provide the relevant
information in case of a failure. Use that and propagate a #GP when the
linear address of an instruction to fetch could not be calculated.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210614135327.9921-7-joro@8bytes.org
---
arch/x86/kernel/sev.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index a1eeaa7..8178db0 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -261,11 +261,18 @@ static enum es_result __vc_decode_user_insn(struct es_em_ctxt *ctxt)
int insn_bytes;

insn_bytes = insn_fetch_from_user_inatomic(ctxt->regs, buffer);
- if (insn_bytes <= 0) {
+ if (insn_bytes == 0) {
+ /* Nothing could be copied */
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;
+ } else if (insn_bytes == -EINVAL) {
+ /* Effective RIP could not be calculated */
+ ctxt->fi.vector = X86_TRAP_GP;
+ ctxt->fi.error_code = 0;
+ ctxt->fi.cr2 = 0;
+ return ES_EXCEPTION;
}

if (!insn_decode_from_regs(&ctxt->insn, ctxt->regs, buffer, insn_bytes))