[PATCH 2/2] livepatch: avoid relocations referencing ignored section symbols

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Track whether symbols belong to ignored sections in order to avoid
applying relocations referencing those symbols. The address of such
symbols won't be resolved and thus the relocation will likely fail or
write garbage to the destination.

Return an error in that case, as leaving unresolved relocations would
lead to malfunctioning payload code.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/arm/arm32/livepatch.c  | 7 +++++++
 xen/arch/arm/arm64/livepatch.c  | 7 +++++++
 xen/arch/x86/livepatch.c        | 7 +++++++
 xen/common/livepatch_elf.c      | 6 ++++++
 xen/include/xen/livepatch_elf.h | 1 +
 5 files changed, 28 insertions(+)

diff --git a/xen/arch/arm/arm32/livepatch.c b/xen/arch/arm/arm32/livepatch.c
index 5a06467008..6aed227818 100644
--- a/xen/arch/arm/arm32/livepatch.c
+++ b/xen/arch/arm/arm32/livepatch.c
@@ -272,6 +272,13 @@ int arch_livepatch_perform(struct livepatch_elf *elf,
                    elf->name, symndx);
             return -EINVAL;
         }
+        else if ( elf->sym[symndx].ignored )
+        {
+            printk(XENLOG_ERR LIVEPATCH
+                    "%s: Relocation against ignored symbol %s cannot be 
resolved\n",
+                    elf->name, elf->sym[symndx].name);
+            return -EINVAL;
+        }
 
         val = elf->sym[symndx].sym->st_value; /* S */
 
diff --git a/xen/arch/arm/arm64/livepatch.c b/xen/arch/arm/arm64/livepatch.c
index 6ec8dc60f0..655ded33d2 100644
--- a/xen/arch/arm/arm64/livepatch.c
+++ b/xen/arch/arm/arm64/livepatch.c
@@ -270,6 +270,13 @@ int arch_livepatch_perform_rela(struct livepatch_elf *elf,
                    elf->name, symndx);
             return -EINVAL;
         }
+        else if ( elf->sym[symndx].ignored )
+        {
+            printk(XENLOG_ERR LIVEPATCH
+                    "%s: Relocation against ignored symbol %s cannot be 
resolved\n",
+                    elf->name, elf->sym[symndx].name);
+            return -EINVAL;
+        }
 
         val = elf->sym[symndx].sym->st_value +  r->r_addend; /* S+A */
 
diff --git a/xen/arch/x86/livepatch.c b/xen/arch/x86/livepatch.c
index 37c9b8435e..a928e5bfcd 100644
--- a/xen/arch/x86/livepatch.c
+++ b/xen/arch/x86/livepatch.c
@@ -262,6 +262,13 @@ int arch_livepatch_perform_rela(struct livepatch_elf *elf,
                    elf->name, symndx);
             return -EINVAL;
         }
+        else if ( elf->sym[symndx].ignored )
+        {
+            printk(XENLOG_ERR LIVEPATCH
+                    "%s: Relocation against ignored symbol %s cannot be 
resolved\n",
+                    elf->name, elf->sym[symndx].name);
+            return -EINVAL;
+        }
 
         val = r->r_addend + elf->sym[symndx].sym->st_value;
 
diff --git a/xen/common/livepatch_elf.c b/xen/common/livepatch_elf.c
index b089cacb1c..45d73912a3 100644
--- a/xen/common/livepatch_elf.c
+++ b/xen/common/livepatch_elf.c
@@ -334,7 +334,13 @@ int livepatch_elf_resolve_symbols(struct livepatch_elf 
*elf)
             }
 
             if ( livepatch_elf_ignore_section(elf->sec[idx].sec) )
+            {
+                dprintk(XENLOG_DEBUG, LIVEPATCH
+                        "%s: Symbol %s from section %s ignored\n",
+                        elf->name, elf->sym[i].name, elf->sec[idx].name);
+                elf->sym[i].ignored = true;
                 break;
+            }
 
             st_value += (unsigned long)elf->sec[idx].load_addr;
             if ( elf->sym[i].name )
diff --git a/xen/include/xen/livepatch_elf.h b/xen/include/xen/livepatch_elf.h
index 5b1ec469da..7116deaddc 100644
--- a/xen/include/xen/livepatch_elf.h
+++ b/xen/include/xen/livepatch_elf.h
@@ -22,6 +22,7 @@ struct livepatch_elf_sec {
 struct livepatch_elf_sym {
     const Elf_Sym *sym;
     const char *name;
+    bool ignored;
 };
 
 struct livepatch_elf {
-- 
2.34.1