From eff53089523c331ac946df74ba365072a6fd1a95 Mon Sep 17 00:00:00 2001 From: David Woodhouse Date: Sun, 28 Apr 2019 13:52:12 +0300 Subject: xen: Avoid overlapping segments in low memory MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Unlike Linux which creates a full identity mapping, Xen only maps those segments which are explicitly requested. Therefore, xen_kexec_load() silently adds in a segment from zero to 1MiB to ensure that VGA memory and other things are accessible. However, this doesn't work when there are already segments to be loaded under 1MiB, because the overlap causes Xen to reject the kexec_load. Be more careful and just infill the ranges which are required instead of naïvely adding a full 0-1MiB segment at the end of the list. Signed-off-by: David Woodhouse Signed-off-by: Simon Horman --- kexec/kexec-xen.c | 73 ++++++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 54 insertions(+), 19 deletions(-) (limited to 'kexec') diff --git a/kexec/kexec-xen.c b/kexec/kexec-xen.c index 1887390..c326955 100644 --- a/kexec/kexec-xen.c +++ b/kexec/kexec-xen.c @@ -64,15 +64,18 @@ int __xc_interface_close(xc_interface *xch) } #endif /* CONFIG_LIBXENCTRL_DL */ +#define IDENTMAP_1MiB (1024 * 1024) + int xen_kexec_load(struct kexec_info *info) { - uint32_t nr_segments = info->nr_segments; + uint32_t nr_segments = info->nr_segments, nr_low_segments = 0; struct kexec_segment *segments = info->segment; + uint64_t low_watermark = 0; xc_interface *xch; xc_hypercall_buffer_array_t *array = NULL; uint8_t type; uint8_t arch; - xen_kexec_segment_t *xen_segs; + xen_kexec_segment_t *xen_segs, *seg; int s; int ret = -1; @@ -80,7 +83,28 @@ int xen_kexec_load(struct kexec_info *info) if (!xch) return -1; - xen_segs = calloc(nr_segments + 1, sizeof(*xen_segs)); + /* + * Ensure 0 - 1 MiB is mapped and accessible by the image. + * This allows access to the VGA memory and the region + * purgatory copies in the crash case. + * + * First, count the number of additional segments which will + * need to be added in between the ones in segments[]. + * + * The segments are already sorted. + */ + for (s = 0; s < nr_segments && (uint64_t)segments[s].mem <= IDENTMAP_1MiB; s++) { + if ((uint64_t)segments[s].mem > low_watermark) + nr_low_segments++; + + low_watermark = (uint64_t)segments[s].mem + segments[s].memsz; + } + if (low_watermark < IDENTMAP_1MiB) + nr_low_segments++; + + low_watermark = 0; + + xen_segs = calloc(nr_segments + nr_low_segments, sizeof(*xen_segs)); if (!xen_segs) goto out; @@ -88,32 +112,43 @@ int xen_kexec_load(struct kexec_info *info) if (array == NULL) goto out; + seg = xen_segs; for (s = 0; s < nr_segments; s++) { DECLARE_HYPERCALL_BUFFER(void, seg_buf); + if (low_watermark < IDENTMAP_1MiB && (uint64_t)segments[s].mem > low_watermark) { + set_xen_guest_handle(seg->buf.h, HYPERCALL_BUFFER_NULL); + seg->buf_size = 0; + seg->dest_maddr = low_watermark; + low_watermark = (uint64_t)segments[s].mem; + if (low_watermark > IDENTMAP_1MiB) + low_watermark = IDENTMAP_1MiB; + seg->dest_size = low_watermark - seg->dest_maddr; + seg++; + } + seg_buf = xc_hypercall_buffer_array_alloc(xch, array, s, seg_buf, segments[s].bufsz); if (seg_buf == NULL) goto out; memcpy(seg_buf, segments[s].buf, segments[s].bufsz); - set_xen_guest_handle(xen_segs[s].buf.h, seg_buf); - xen_segs[s].buf_size = segments[s].bufsz; - xen_segs[s].dest_maddr = (uint64_t)segments[s].mem; - xen_segs[s].dest_size = segments[s].memsz; + set_xen_guest_handle(seg->buf.h, seg_buf); + seg->buf_size = segments[s].bufsz; + seg->dest_maddr = (uint64_t)segments[s].mem; + seg->dest_size = segments[s].memsz; + seg++; + + low_watermark = (uint64_t)segments[s].mem + segments[s].memsz; } - /* - * Ensure 0 - 1 MiB is mapped and accessible by the image. - * - * This allows access to the VGA memory and the region - * purgatory copies in the crash case. - */ - set_xen_guest_handle(xen_segs[s].buf.h, HYPERCALL_BUFFER_NULL); - xen_segs[s].buf_size = 0; - xen_segs[s].dest_maddr = 0; - xen_segs[s].dest_size = 1 * 1024 * 1024; - nr_segments++; + if ((uint64_t)low_watermark < IDENTMAP_1MiB) { + set_xen_guest_handle(seg->buf.h, HYPERCALL_BUFFER_NULL); + seg->buf_size = 0; + seg->dest_maddr = low_watermark; + seg->dest_size = IDENTMAP_1MiB - low_watermark; + seg++; + } type = (info->kexec_flags & KEXEC_ON_CRASH) ? KEXEC_TYPE_CRASH : KEXEC_TYPE_DEFAULT; @@ -125,7 +160,7 @@ int xen_kexec_load(struct kexec_info *info) #endif ret = xc_kexec_load(xch, type, arch, (uint64_t)info->entry, - nr_segments, xen_segs); + nr_segments + nr_low_segments, xen_segs); out: xc_hypercall_buffer_array_destroy(xch, array); -- cgit