iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

x86/sev: Disable MMIO emulation from user mode

Browse Source 
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 <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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Borislav Petkov (AMD) 2023-10-05 11:06:36 +02:00 committed by Greg Kroah-Hartman
parent 0b4e772a6a
commit 6797c6d09e
1 changed files with 3 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/x86/kernel/sev.c
View File

@ -1004,6 +1004,9 @@ static enum es_result vc_handle_mmio(struct ghcb *ghcb,
enum es_result ret;
long *reg_data;
if (user_mode(ctxt->regs))
return ES_UNSUPPORTED;
switch (insn->opcode.bytes[0]) {
/* MMIO Write */
case 0x88: