From 95ff590b802757f8b6bd32e7e5b21ef9b91e2583 Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" Date: Thu, 5 Oct 2023 11:06:36 +0200 Subject: [PATCH] x86/sev: Disable MMIO emulation from user mode Upstream commit: a37cd2a59d0cb270b1bba568fd3a3b8668b9d3ba A virt scenario can be constructed where MMIO memory can be user memory. When that happens, a race condition opens between when the hardware raises the #VC and when the #VC handler gets to emulate the instruction. If the MOVS is replaced with a MOVS accessing kernel memory in that small race window, then write to kernel memory happens as the access checks are not done at emulation time. Disable MMIO emulation in user mode temporarily until a sensible use case appears and justifies properly handling the race window. Fixes: 0118b604c2c9 ("x86/sev-es: Handle MMIO String Instructions") Reported-by: Tom Dohrmann Signed-off-by: Borislav Petkov (AMD) Tested-by: Tom Dohrmann Cc: Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/sev.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index afda719..6a8668e 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -1552,6 +1552,9 @@ static enum es_result vc_handle_mmio(struct ghcb *ghcb, struct es_em_ctxt *ctxt) return ES_DECODE_FAILED; } + if (user_mode(ctxt->regs)) + return ES_UNSUPPORTED; + switch (mmio) { case MMIO_WRITE: memcpy(ghcb->shared_buffer, reg_data, bytes); -- 2.7.4