[xen master] libelf: improve PVH elfnote parsing

[patchbot@xxxxxxx]

commit 632cbaf1243e4b867caf321cfef81517f5cc27ad
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Fri May 28 09:14:44 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri May 28 09:14:44 2021 +0200

    libelf: improve PVH elfnote parsing
    
    Pass an hvm boolean parameter to the elf note checking routines, so that
    better checking can be done in case libelf is dealing with an hvm
    container.
    
    elf_xen_note_check shouldn't return early unless PHYS32_ENTRY is set
    and the container is of type HVM, or else the loader and version
    checks would be avoided for kernels intended to be booted as PV but
    that also have PHYS32_ENTRY set.
    
    Adjust elf_xen_addr_calc_check so that the virtual addresses are
    actually physical ones (by setting virt_base and elf_paddr_offset to
    zero) when the container is of type HVM, as that container is always
    started with paging disabled.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/common/libelf/libelf-dominfo.c | 41 ++++++++++++++++++++++++--------------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/xen/common/libelf/libelf-dominfo.c 
b/xen/common/libelf/libelf-dominfo.c
index bd295a9b7e..24d1371dd7 100644
--- a/xen/common/libelf/libelf-dominfo.c
+++ b/xen/common/libelf/libelf-dominfo.c
@@ -360,7 +360,7 @@ elf_errorstatus elf_xen_parse_guest_info(struct elf_binary 
*elf,
 /* sanity checks                                                            */
 
 static elf_errorstatus elf_xen_note_check(struct elf_binary *elf,
-                              struct elf_dom_parms *parms)
+                              struct elf_dom_parms *parms, bool hvm)
 {
     if ( (ELF_PTRVAL_INVALID(parms->elf_note_start)) &&
          (ELF_PTRVAL_INVALID(parms->guest_info)) )
@@ -382,7 +382,7 @@ static elf_errorstatus elf_xen_note_check(struct elf_binary 
*elf,
     }
 
     /* PVH only requires one ELF note to be set */
-    if ( parms->phys_entry != UNSET_ADDR32 )
+    if ( parms->phys_entry != UNSET_ADDR32 && hvm )
     {
         elf_msg(elf, "ELF: Found PVH image\n");
         return 0;
@@ -414,7 +414,7 @@ static elf_errorstatus elf_xen_note_check(struct elf_binary 
*elf,
 }
 
 static elf_errorstatus elf_xen_addr_calc_check(struct elf_binary *elf,
-                                   struct elf_dom_parms *parms)
+                                   struct elf_dom_parms *parms, bool hvm)
 {
     uint64_t virt_offset;
 
@@ -425,12 +425,15 @@ static elf_errorstatus elf_xen_addr_calc_check(struct 
elf_binary *elf,
         return -1;
     }
 
-    /* Initial guess for virt_base is 0 if it is not explicitly defined. */
-    if ( parms->virt_base == UNSET_ADDR )
+    /*
+     * Initial guess for virt_base is 0 if it is not explicitly defined in the
+     * PV case. For PVH virt_base is forced to 0 because paging is disabled.
+     */
+    if ( parms->virt_base == UNSET_ADDR || hvm )
     {
         parms->virt_base = 0;
-        elf_msg(elf, "ELF: VIRT_BASE unset, using %#" PRIx64 "\n",
-                parms->virt_base);
+        if ( !hvm )
+            elf_msg(elf, "ELF: VIRT_BASE unset, using 0\n");
     }
 
     /*
@@ -441,23 +444,31 @@ static elf_errorstatus elf_xen_addr_calc_check(struct 
elf_binary *elf,
      *
      * If we are using the modern ELF notes interface then the default
      * is 0.
+     *
+     * For PVH this is forced to 0, as it's already a legacy option for PV.
      */
-    if ( parms->elf_paddr_offset == UNSET_ADDR )
+    if ( parms->elf_paddr_offset == UNSET_ADDR || hvm )
     {
-        if ( parms->elf_note_start )
+        if ( parms->elf_note_start || hvm )
             parms->elf_paddr_offset = 0;
         else
             parms->elf_paddr_offset = parms->virt_base;
-        elf_msg(elf, "ELF_PADDR_OFFSET unset, using %#" PRIx64 "\n",
-                parms->elf_paddr_offset);
+        if ( !hvm )
+            elf_msg(elf, "ELF_PADDR_OFFSET unset, using %#" PRIx64 "\n",
+                    parms->elf_paddr_offset);
     }
 
     virt_offset = parms->virt_base - parms->elf_paddr_offset;
     parms->virt_kstart = elf->pstart + virt_offset;
     parms->virt_kend   = elf->pend   + virt_offset;
 
-    if ( parms->virt_entry == UNSET_ADDR )
-        parms->virt_entry = elf_uval(elf, elf->ehdr, e_entry);
+    if ( parms->virt_entry == UNSET_ADDR || hvm )
+    {
+        if ( parms->phys_entry != UNSET_ADDR32 && hvm )
+            parms->virt_entry = parms->phys_entry;
+        else
+            parms->virt_entry = elf_uval(elf, elf->ehdr, e_entry);
+    }
 
     if ( parms->bsd_symtab )
     {
@@ -592,9 +603,9 @@ elf_errorstatus elf_xen_parse(struct elf_binary *elf,
         }
     }
 
-    if ( elf_xen_note_check(elf, parms) != 0 )
+    if ( elf_xen_note_check(elf, parms, hvm) != 0 )
         return -1;
-    if ( elf_xen_addr_calc_check(elf, parms) != 0 )
+    if ( elf_xen_addr_calc_check(elf, parms, hvm) != 0 )
         return -1;
     return 0;
 }
--
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