From ef6cb76026628e26e3d1ae53c50ccde1c3c78b1b Mon Sep 17 00:00:00 2001 From: Jim Fehlig Date: Thu, 12 Nov 2015 19:40:46 -0700 Subject: [PATCH] libxl: relax readonly check introduced by XSA-142 fix The fix for XSA-142 is quite a big hammer, rejecting readonly disk configuration even when the requested backend is known to support readonly. While it is true that qemu doesn't support readonly for emulated IDE or AHCI disks $ /usr/lib/xen/bin/qemu-system-i386 \ -drive file=/tmp/disk.raw,if=ide,media=disk,format=raw,readonly=on qemu-system-i386: Can't use a read-only drive $ /usr/lib/xen/bin/qemu-system-i386 -device ahci,id=ahci0 \ -drive file=/tmp/disk.raw,if=none,id=ahcidisk-0,format=raw,readonly=on \ -device ide-hd,bus=ahci0.0,unit=0,drive=ahcidisk-0 qemu-system-i386: -device ide-hd,bus=ahci0.0,unit=0,drive=ahcidisk-0: Can't use a read-only drive It does support readonly SCSI disks $ /usr/lib/xen/bin/qemu-system-i386 \ -drive file=/tmp/disk.raw,if=scsi,media=disk,format=raw,readonly=on [ok] Inside a guest using such a disk, the SCSI kernel driver sees write protect on [ 7.339232] sd 2:0:1:0: [sdb] Write Protect is on Also, PV drivers support readonly, but the patch rejects such configuration even when PV drivers (vdev=xvd*) have been explicitly specified and creation of an emulated twin is skiped. This follow-up patch loosens the restriction to reject readonly when creating an emulated IDE or AHCI disk, but allows it when the backend is known to support readonly. Signed-off-by: Jim Fehlig Acked-by: Stefano Stabellini Acked-by: Ian Campbell --- tools/libxl/libxl_dm.c | 29 ++++++++++++++++------------- 1 file changed, 16 insertions(+), 13 deletions(-) diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c index 151b6ed86e..175accd8e7 100644 --- a/tools/libxl/libxl_dm.c +++ b/tools/libxl/libxl_dm.c @@ -1185,12 +1185,6 @@ static int libxl__build_device_model_args_new(libxl__gc *gc, (gc, "file=%s,if=ide,index=%d,readonly=%s,media=cdrom,format=%s,cache=writeback,id=ide-%i", disks[i].pdev_path, disk, disks[i].readwrite ? "off" : "on", format, dev_number); } else { - if (!disks[i].readwrite) { - LOG(ERROR, - "qemu-xen doesn't support read-only disk drivers"); - return ERROR_INVAL; - } - if (disks[i].format == LIBXL_DISK_FORMAT_EMPTY) { LOG(WARN, "cannot support"" empty disk format for %s", disks[i].vdev); @@ -1218,29 +1212,38 @@ static int libxl__build_device_model_args_new(libxl__gc *gc, * For other disks we translate devices 0..3 into * hd[a-d] and ignore the rest. */ - if (strncmp(disks[i].vdev, "sd", 2) == 0) + if (strncmp(disks[i].vdev, "sd", 2) == 0) { drive = libxl__sprintf - (gc, "file=%s,if=scsi,bus=0,unit=%d,format=%s,cache=writeback", - pdev_path, disk, format); - else if (strncmp(disks[i].vdev, "xvd", 3) == 0) + (gc, "file=%s,if=scsi,bus=0,unit=%d,format=%s,readonly=%s,cache=writeback", + pdev_path, disk, format, disks[i].readwrite ? "off" : "on"); + } else if (strncmp(disks[i].vdev, "xvd", 3) == 0) { /* * Do not add any emulated disk when PV disk are * explicitly asked for. */ continue; - else if (disk < 6 && b_info->u.hvm.hdtype == LIBXL_HDTYPE_AHCI) { + } else if (disk < 6 && b_info->u.hvm.hdtype == LIBXL_HDTYPE_AHCI) { + if (!disks[i].readwrite) { + LOG(ERROR, "qemu-xen doesn't support read-only AHCI disk drivers"); + return ERROR_INVAL; + } flexarray_vappend(dm_args, "-drive", GCSPRINTF("file=%s,if=none,id=ahcidisk-%d,format=%s,cache=writeback", pdev_path, disk, format), "-device", GCSPRINTF("ide-hd,bus=ahci0.%d,unit=0,drive=ahcidisk-%d", disk, disk), NULL); continue; - } else if (disk < 4) + } else if (disk < 4) { + if (!disks[i].readwrite) { + LOG(ERROR, "qemu-xen doesn't support read-only IDE disk drivers"); + return ERROR_INVAL; + } drive = libxl__sprintf (gc, "file=%s,if=ide,index=%d,media=disk,format=%s,cache=writeback", pdev_path, disk, format); - else + } else { continue; /* Do not emulate this disk */ + } } flexarray_append(dm_args, "-drive"); -- 2.39.5