[PATCH] xen: consider alloc-only segments when loading PV dom0 kernel

[Juergen Gross <jgross@xxxxxxxx>]

When loading the dom0 kernel for PV mode, the first free usable memory
location after the kernel needs to take segments into account, which
have only the ALLOC flag set, but are not specified to be loaded in
the program headers of the ELF file.

This is e.g. a problem for Linux kernels from 5.19 onwards, as those
can have a final NOLOAD section at the end, which must not be used by
e.g. the start_info structure or the initial page tables allocated by
the hypervisor.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/common/libelf/libelf-loader.c | 33 +++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/xen/common/libelf/libelf-loader.c 
b/xen/common/libelf/libelf-loader.c
index 629cc0d3e6..4b0e3ced55 100644
--- a/xen/common/libelf/libelf-loader.c
+++ b/xen/common/libelf/libelf-loader.c
@@ -467,7 +467,9 @@ do {                                                        
        \
 void elf_parse_binary(struct elf_binary *elf)
 {
     ELF_HANDLE_DECL(elf_phdr) phdr;
+    ELF_HANDLE_DECL(elf_shdr) shdr;
     uint64_t low = -1, high = 0, paddr, memsz;
+    uint64_t vlow = -1, vhigh = 0, vaddr, voff;
     unsigned i, count;
 
     count = elf_phdr_count(elf);
@@ -480,6 +482,7 @@ void elf_parse_binary(struct elf_binary *elf)
         if ( !elf_phdr_is_loadable(elf, phdr) )
             continue;
         paddr = elf_uval(elf, phdr, p_paddr);
+        vaddr = elf_uval(elf, phdr, p_vaddr);
         memsz = elf_uval(elf, phdr, p_memsz);
         elf_msg(elf, "ELF: phdr: paddr=%#" PRIx64 " memsz=%#" PRIx64 "\n",
                 paddr, memsz);
@@ -487,7 +490,37 @@ void elf_parse_binary(struct elf_binary *elf)
             low = paddr;
         if ( high < paddr + memsz )
             high = paddr + memsz;
+        if ( vlow > vaddr )
+            vlow = vaddr;
+        if ( vhigh < vaddr + memsz )
+            vhigh = vaddr + memsz;
     }
+
+    voff = vhigh - high;
+
+    count = elf_shdr_count(elf);
+    for ( i = 0; i < count; i++ )
+    {
+        shdr = elf_shdr_by_index(elf, i);
+        if ( !elf_access_ok(elf, ELF_HANDLE_PTRVAL(shdr), 1) )
+            /* input has an insane section header count field */
+            break;
+        if ( !(elf_uval(elf, shdr, sh_flags) & SHF_ALLOC) )
+            continue;
+        vaddr = elf_uval(elf, shdr, sh_addr);
+        memsz = elf_uval(elf, shdr, sh_size);
+        if ( vlow > vaddr )
+        {
+            vlow = vaddr;
+            low = vaddr - voff;
+        }
+        if ( vhigh < vaddr + memsz )
+        {
+            vhigh = vaddr + memsz;
+            high = vaddr + memsz - voff;
+        }
+    }
+
     elf->pstart = low;
     elf->pend = high;
     elf_msg(elf, "ELF: memory: %#" PRIx64 " -> %#" PRIx64 "\n",
-- 
2.35.3