[PATCH v6 51/76] x86/sev-es: Handle instruction fetches from user-space

Joerg Roedel
2020-08-24T09:08:44Z

From: Joerg Roedel <jroedel@suse.de>

When a #VC exception is triggered by user-space the instruction decoder
needs to read the instruction bytes from user addresses. Enhance
vc_decode_insn() to safely fetch kernel and user instructions.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20200724160336.5435-51-joro@8bytes.org
---
arch/x86/kernel/sev-es.c | 31 ++++++++++++++++++++++---------
1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 81d94f78d2d4..1493e8cf14f2 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -237,17 +237,30 @@ static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
enum es_result ret;
int res;

- res = vc_fetch_insn_kernel(ctxt, buffer);
- if (unlikely(res == -EFAULT)) {
- ctxt->fi.vector = X86_TRAP_PF;
- ctxt->fi.error_code = 0;
- ctxt->fi.cr2 = ctxt->regs->ip;
- return ES_EXCEPTION;
+ if (user_mode(ctxt->regs)) {
+ res = insn_fetch_from_user(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;
+ }
+
+ if (!insn_decode(&ctxt->insn, ctxt->regs, buffer, res))
+ return ES_DECODE_FAILED;
+ } else {
+ res = vc_fetch_insn_kernel(ctxt, buffer);
+ if (res) {
+ ctxt->fi.vector = X86_TRAP_PF;
+ ctxt->fi.error_code = X86_PF_INSTR;
+ ctxt->fi.cr2 = ctxt->regs->ip;
+ return ES_EXCEPTION;
+ }
+
+ insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
+ insn_get_length(&ctxt->insn);
}

- insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
- insn_get_length(&ctxt->insn);
-
ret = ctxt->insn.immediate.got ? ES_OK : ES_DECODE_FAILED;

return ret;
--
2.28.0