livepatch/arm/x86: Check payload for for unwelcomed symbols.

Certain platforms, such as ARM [32|64] add extra mapping symbols
such as $x (for ARM64 instructions), or more interesting to
this patch: $t (for Thumb instructions). These symbols are supposed
to help the final linker to make any adjustments (such as
add an veneer). But more importantly - we do not compile Xen
with any Thumb instructions (which are variable length) - and
if we find these mapping symbols we should disallow such payload.

Reviewed-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/xen/arch/arm/arm32/livepatch.c b/xen/arch/arm/arm32/livepatch.c
index 80f9646e01220efedace3d093d90f412c76baa95..5fc2e634514720e1b604bd117989e7a923313786 100644 (file)
--- a/xen/arch/arm/arm32/livepatch.c
+++ b/xen/arch/arm/arm32/livepatch.c
@@ -20,6 +20,19 @@ int arch_livepatch_verify_elf(const struct livepatch_elf *elf)
     return -EOPNOTSUPP;
 }
 
+bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf,
+                                const struct livepatch_elf_sym *sym)
+{
+    /*
+     * Xen does not use Thumb instructions - and we should not see any of
+     * them. If we do, abort.
+     */
+    if ( sym->name && sym->name[0] == '$' && sym->name[1] == 't' )
+        return ( !sym->name[2] || sym->name[2] == '.' );
+
+    return false;
+}
+
 int arch_livepatch_perform_rela(struct livepatch_elf *elf,
                                 const struct livepatch_elf_sec *base,
                                 const struct livepatch_elf_sec *rela)

diff --git a/xen/arch/arm/arm64/livepatch.c b/xen/arch/arm/arm64/livepatch.c
index 774f845a916e61e1a71790ec64187ed3a5f3923b..f1489272448c6a5bdf0b6c1b0c3c9494fb155d07 100644 (file)
--- a/xen/arch/arm/arm64/livepatch.c
+++ b/xen/arch/arm/arm64/livepatch.c
@@ -90,6 +90,13 @@ int arch_livepatch_verify_elf(const struct livepatch_elf *elf)
     return 0;
 }
 
+bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf,
+                                const struct livepatch_elf_sym *sym)
+{
+    /* No special checks on ARM 64. */
+    return false;
+}
+
 enum aarch64_reloc_op {
     RELOC_OP_NONE,
     RELOC_OP_ABS,

diff --git a/xen/arch/x86/livepatch.c b/xen/arch/x86/livepatch.c
index 7a369a004b9d47a8e8c5ed171488f8ec51d658b5..9663ef6fef6b860f6882c998e52c4d9d4a252e95 100644 (file)
--- a/xen/arch/x86/livepatch.c
+++ b/xen/arch/x86/livepatch.c
@@ -131,6 +131,13 @@ bool arch_livepatch_symbol_ok(const struct livepatch_elf *elf,
     return true;
 }
 
+bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf,
+                                const struct livepatch_elf_sym *sym)
+{
+    /* No special checks on x86. */
+    return false;
+}
+
 int arch_livepatch_perform_rel(struct livepatch_elf *elf,
                                const struct livepatch_elf_sec *base,
                                const struct livepatch_elf_sec *rela)

diff --git a/xen/common/livepatch_elf.c b/xen/common/livepatch_elf.c
index dec904a48f027bb574dd2ff77635f0a806037b3b..c4a9633078434630c922c1f1291295d0767d5b9d 100644 (file)
--- a/xen/common/livepatch_elf.c
+++ b/xen/common/livepatch_elf.c
@@ -251,6 +251,12 @@ static int elf_get_sym(struct livepatch_elf *elf, const void *data)
 
         sym[i].sym = s;
         sym[i].name = strtab_sec->data + delta;
+        if ( arch_livepatch_symbol_deny(elf, &sym[i]) )
+        {
+            dprintk(XENLOG_ERR, LIVEPATCH "%s: Symbol '%s' should not be in payload!\n",
+                    elf->name, sym[i].name);
+            return -EINVAL;
+        }
     }
     elf->nsym = nsym;
 

diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h
index e8c67d6b0193c963cb4edd679014e7e573938dd0..98ec01216bc3634a82f029b177011b0cc8fbfcf5 100644 (file)
--- a/xen/include/xen/livepatch.h
+++ b/xen/include/xen/livepatch.h
@@ -50,6 +50,8 @@ bool_t is_patch(const void *addr);
 int arch_livepatch_verify_elf(const struct livepatch_elf *elf);
 bool arch_livepatch_symbol_ok(const struct livepatch_elf *elf,
                               const struct livepatch_elf_sym *sym);
+bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf,
+                                const struct livepatch_elf_sym *sym);
 int arch_livepatch_perform_rel(struct livepatch_elf *elf,
                                const struct livepatch_elf_sec *base,
                                const struct livepatch_elf_sec *rela);