5.15-stable review patch. If anyone has any objections, please let me know.
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From: "Borislav Petkov (AMD)" bp@alien8.de
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 --- arch/x86/kernel/sev.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -1004,6 +1004,9 @@ static enum es_result vc_handle_mmio(str enum es_result ret; long *reg_data;
+ if (user_mode(ctxt->regs)) + return ES_UNSUPPORTED; + switch (insn->opcode.bytes[0]) { /* MMIO Write */ case 0x88: