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[SRU,Lunar/Mantic/OEM-6.5,1/3] x86/sev: Disable MMIO emulation from user mode

Message ID 20231201131601.1146971-3-magali.lemes@canonical.com
State New
Headers show
Series [SRU,Lunar/Mantic/OEM-6.5,1/3] x86/sev: Disable MMIO emulation from user mode | expand

Commit Message

Magali Lemes Dec. 1, 2023, 1:15 p.m. UTC 
From: "Borislav Petkov (AMD)" <bp@alien8.de>

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 <erbse.13@gmx.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Tom Dohrmann <erbse.13@gmx.de>
Cc: <stable@kernel.org>
(cherry picked from commit a37cd2a59d0cb270b1bba568fd3a3b8668b9d3ba)
CVE-2023-46813
Signed-off-by: Magali Lemes <magali.lemes@canonical.com>
---
 arch/x86/kernel/sev.c | 3 +++
 1 file changed, 3 insertions(+)
diff mbox series

Patch

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 45ef3926381f..b09172592e02 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 INSN_MMIO_WRITE:
 		memcpy(ghcb->shared_buffer, reg_data, bytes);