Oops, $subject should have said [PATCH, v3] ...
>>> On 19.07.11 at 15:16, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
> With our switching away from supporting 32-bit Dom0 operation, users
> complained that attempts (perhaps due to lack of knowledge of that
> change) to boot the no longer privileged kernel in Dom0 resulted in
> apparently silent failure. To make the mismatch explicit and visible,
> add feature flags that the kernel can set to indicate operation in
> what modes it supports. For backward compatibility, absence of both
> feature flags is taken to indicate a kernel that may be capable of
> operating in both modes.
>
> v2: Due to the way elf_xen_parse_features() worked up to now (getting
> fixed here), adding features indications to the old, string based ELF
> note would make the respective kernel unusable on older hypervisors.
> For that reason, a new ELF Note is being introduced that allows
> specifying supported features as a bit array instead (with features
> unknown to the hypervisor simply ignored, as now also done by
> elf_xen_parse_features(), whereas here unknown kernel-required
> features still keep the kernel [and hence VM] from booting).
>
> v3: Introduce and use elf_note_numeric_array() to be forward
> compatible (or else an old hypervisor wouldn't be able to parse kernel
> specified features occupying more than 64 bits - thanks, Ian!).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
>
> --- a/tools/libxc/xc_dom_elfloader.c
> +++ b/tools/libxc/xc_dom_elfloader.c
> @@ -286,6 +286,15 @@ static int xc_dom_parse_elf_kernel(struc
> if ( (rc = elf_xen_parse(elf, &dom->parms)) != 0 )
> return rc;
>
> + if ( elf_xen_feature_get(XENFEAT_privileged, dom->parms.f_required) ||
> + (elf_xen_feature_get(XENFEAT_privileged, dom->parms.f_supported) &&
> + !elf_xen_feature_get(XENFEAT_unprivileged,
> dom->parms.f_supported))
> )
> + {
> + xc_dom_panic(dom->xch, XC_INVALID_KERNEL, "%s: Kernel does not"
> + " support unprivileged (DomU) operation",
> __FUNCTION__);
> + return -EINVAL;
> + }
> +
> /* find kernel segment */
> dom->kernel_seg.vstart = dom->parms.virt_kstart;
> dom->kernel_seg.vend = dom->parms.virt_kend;
> --- a/xen/arch/ia64/xen/domain.c
> +++ b/xen/arch/ia64/xen/domain.c
> @@ -2164,6 +2164,14 @@ int __init construct_dom0(struct domain
> return -1;
> }
>
> + if (test_bit(XENFEAT_unprivileged, parms.f_required) ||
> + (test_bit(XENFEAT_unprivileged, parms.f_supported) &&
> + !test_bit(XENFEAT_privileged, parms.f_supported)))
> + {
> + printk("Kernel does not support Dom0 operation\n");
> + return -1;
> + }
> +
> p_start = parms.virt_base;
> pkern_start = parms.virt_kstart;
> pkern_end = parms.virt_kend;
> --- a/xen/arch/x86/domain_build.c
> +++ b/xen/arch/x86/domain_build.c
> @@ -415,6 +415,14 @@ int __init construct_dom0(
> return -EINVAL;
> }
>
> + if ( test_bit(XENFEAT_unprivileged, parms.f_required) ||
> + (test_bit(XENFEAT_unprivileged, parms.f_supported) &&
> + !test_bit(XENFEAT_privileged, parms.f_supported)) )
> + {
> + printk("Kernel does not support Dom0 operation\n");
> + return -EINVAL;
> + }
> +
> #if defined(__x86_64__)
> if ( compat32 )
> {
> --- a/xen/common/kernel.c
> +++ b/xen/common/kernel.c
> @@ -278,7 +278,8 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDL
> switch ( fi.submap_idx )
> {
> case 0:
> - fi.submap = 0;
> + fi.submap = 1U << (IS_PRIV(current->domain) ?
> + XENFEAT_privileged : XENFEAT_unprivileged);
> if ( VM_ASSIST(d, VMASST_TYPE_pae_extended_cr3) )
> fi.submap |= (1U << XENFEAT_pae_pgdir_above_4gb);
> if ( paging_mode_translate(current->domain) )
> --- a/xen/common/libelf/libelf-dominfo.c
> +++ b/xen/common/libelf/libelf-dominfo.c
> @@ -26,7 +26,9 @@ static const char *const elf_xen_feature
> [XENFEAT_writable_descriptor_tables] = "writable_descriptor_tables",
> [XENFEAT_auto_translated_physmap] = "auto_translated_physmap",
> [XENFEAT_supervisor_mode_kernel] = "supervisor_mode_kernel",
> - [XENFEAT_pae_pgdir_above_4gb] = "pae_pgdir_above_4gb"
> + [XENFEAT_pae_pgdir_above_4gb] = "pae_pgdir_above_4gb",
> + [XENFEAT_privileged] = "privileged",
> + [XENFEAT_unprivileged] = "unprivileged"
> };
> static const int elf_xen_features =
> sizeof(elf_xen_feature_names) / sizeof(elf_xen_feature_names[0]);
> @@ -83,7 +85,7 @@ int elf_xen_parse_features(const char *f
> }
> }
> }
> - if ( i == elf_xen_features )
> + if ( i == elf_xen_features && required && feature[0] == '!' )
> return -1;
> }
>
> @@ -114,6 +116,7 @@ int elf_xen_parse_note(struct elf_binary
> [XEN_ELFNOTE_LOADER] = { "LOADER", 1},
> [XEN_ELFNOTE_PAE_MODE] = { "PAE_MODE", 1},
> [XEN_ELFNOTE_FEATURES] = { "FEATURES", 1},
> + [XEN_ELFNOTE_SUPPORTED_FEATURES] = { "SUPPORTED_FEATURES", 0},
> [XEN_ELFNOTE_BSD_SYMTAB] = { "BSD_SYMTAB", 1},
> [XEN_ELFNOTE_SUSPEND_CANCEL] = { "SUSPEND_CANCEL", 0 },
> [XEN_ELFNOTE_MOD_START_PFN] = { "MOD_START_PFN", 0 },
> @@ -122,6 +125,7 @@ int elf_xen_parse_note(struct elf_binary
>
> const char *str = NULL;
> uint64_t val = 0;
> + unsigned int i;
> int type = elf_uval(elf, note, type);
>
> if ( (type >= sizeof(note_desc) / sizeof(note_desc[0])) ||
> @@ -200,6 +204,12 @@ int elf_xen_parse_note(struct elf_binary
> return -1;
> break;
>
> + case XEN_ELFNOTE_SUPPORTED_FEATURES:
> + for ( i = 0; i < XENFEAT_NR_SUBMAPS; ++i )
> + parms->f_supported[i] |= elf_note_numeric_array(
> + elf, note, sizeof(*parms->f_supported), i);
> + break;
> +
> }
> return 0;
> }
> --- a/xen/common/libelf/libelf-tools.c
> +++ b/xen/common/libelf/libelf-tools.c
> @@ -227,6 +227,27 @@ uint64_t elf_note_numeric(struct elf_bin
> return 0;
> }
> }
> +
> +uint64_t elf_note_numeric_array(struct elf_binary *elf, const elf_note
> *note,
> + unsigned int unitsz, unsigned int idx)
> +{
> + const void *desc = elf_note_desc(elf, note);
> + int descsz = elf_uval(elf, note, descsz);
> +
> + if ( descsz % unitsz || idx >= descsz / unitsz )
> + return 0;
> + switch (unitsz)
> + {
> + case 1:
> + case 2:
> + case 4:
> + case 8:
> + return elf_access_unsigned(elf, desc, idx * unitsz, unitsz);
> + default:
> + return 0;
> + }
> +}
> +
> const elf_note *elf_note_next(struct elf_binary *elf, const elf_note *
> note)
> {
> int namesz = (elf_uval(elf, note, namesz) + 3) & ~3;
> --- a/xen/include/public/elfnote.h
> +++ b/xen/include/public/elfnote.h
> @@ -179,9 +179,22 @@
> #define XEN_ELFNOTE_MOD_START_PFN 16
>
> /*
> + * The features supported by this kernel (numeric).
> + *
> + * Other than XEN_ELFNOTE_FEATURES on pre-4.2 Xen, this note allows a
> + * kernel to specify support for features that older hypervisors don't
> + * know about. The set of features 4.2 and newer hypervisors will
> + * consider supported by the kernel is the combination of the sets
> + * specified through this and the string note.
> + *
> + * LEGACY: FEATURES
> + */
> +#define XEN_ELFNOTE_SUPPORTED_FEATURES 17
> +
> +/*
> * The number of the highest elfnote defined.
> */
> -#define XEN_ELFNOTE_MAX XEN_ELFNOTE_MOD_START_PFN
> +#define XEN_ELFNOTE_MAX XEN_ELFNOTE_SUPPORTED_FEATURES
>
> /*
> * System information exported through crash notes.
> --- a/xen/include/public/features.h
> +++ b/xen/include/public/features.h
> @@ -75,7 +75,13 @@
> #define XENFEAT_hvm_safe_pvclock 9
>
> /* x86: pirq can be used by HVM guests */
> -#define XENFEAT_hvm_pirqs 10
> +#define XENFEAT_hvm_pirqs 10
> +
> +/* privileged operation is supported */
> +#define XENFEAT_privileged 11
> +
> +/* un-privileged operation is supported */
> +#define XENFEAT_unprivileged 12
>
> #define XENFEAT_NR_SUBMAPS 1
>
> --- a/xen/include/xen/libelf.h
> +++ b/xen/include/xen/libelf.h
> @@ -179,6 +179,8 @@ const elf_sym *elf_sym_by_index(struct e
> const char *elf_note_name(struct elf_binary *elf, const elf_note * note);
> const void *elf_note_desc(struct elf_binary *elf, const elf_note * note);
> uint64_t elf_note_numeric(struct elf_binary *elf, const elf_note * note);
> +uint64_t elf_note_numeric_array(struct elf_binary *, const elf_note *,
> + unsigned int unitsz, unsigned int idx);
> const elf_note *elf_note_next(struct elf_binary *elf, const elf_note *
> note);
>
> int elf_is_elfbinary(const void *image);
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