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Subject[tip: x86/seves] x86/sev-es: Handle instruction fetches from user-space
The following commit has been merged into the x86/seves branch of tip:

Commit-ID: 5e3427a7bc432ed2e5de394ac30f160cc6c37a1f
Gitweb: https://git.kernel.org/tip/5e3427a7bc432ed2e5de394ac30f160cc6c37a1f
Author: Joerg Roedel <jroedel@suse.de>
AuthorDate: Mon, 07 Sep 2020 15:15:49 +02:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Wed, 09 Sep 2020 11:33:19 +02:00

x86/sev-es: Handle instruction fetches from user-space

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>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-49-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 b10a62a..6c30dbc 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -232,17 +232,30 @@ 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;
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