Certain platforms, such as ARM [32|64] add extra mapping symbols
such as $x (for ARM64 instructions), or more interesting to
this patch: $t (for Thumb instructions). These symbols are suppose
to help the final linker to make any adjustments (such as
add an veneer). But more importantly - we do not compile Xen
with any Thumb instructions (which are variable length) - and
if we find these mapping symbols we should disallow such payload.
Signed-off-by: Konrad Rzeszutek Wilk
---
Cc: Konrad Rzeszutek Wilk
Cc: Ross Lagerwall
Cc: Stefano Stabellini
Cc: Julien Grall
Cc: Andrew Cooper
v3: New submission.
Use &sym[i] instead of sym (as that will always be NULL).
---
xen/arch/arm/livepatch.c| 14 ++
xen/arch/x86/livepatch.c| 7 +++
xen/common/livepatch_elf.c | 9 +
xen/include/xen/livepatch.h | 2 ++
4 files changed, 32 insertions(+)
diff --git a/xen/arch/arm/livepatch.c b/xen/arch/arm/livepatch.c
index d2ae128..dd94c94 100644
--- a/xen/arch/arm/livepatch.c
+++ b/xen/arch/arm/livepatch.c
@@ -117,6 +117,20 @@ bool_t arch_livepatch_symbol_ok(const struct livepatch_elf
*elf,
return true;
}
+int arch_livepatch_symbol_check(const struct livepatch_elf *elf,
+const struct livepatch_elf_sym *sym)
+{
+#ifdef CONFIG_ARM_32
+/*
+ * Xen does not use Thumb instructions - and we should not see any of
+ * them. If we do, abort.
+ */
+if ( sym->name && *sym->name == '$' && sym->name[1] == 't' )
+return -EINVAL;
+#endif
+return 0;
+}
+
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/arch/x86/livepatch.c b/xen/arch/x86/livepatch.c
index bbcb5fe..27d4aac 100644
--- a/xen/arch/x86/livepatch.c
+++ b/xen/arch/x86/livepatch.c
@@ -125,6 +125,13 @@ bool_t arch_livepatch_symbol_ok(const struct livepatch_elf
*elf,
return true;
}
+int arch_livepatch_symbol_check(const struct livepatch_elf *elf,
+const struct livepatch_elf_sym *sym)
+{
+/* No special checks on x86. */
+return 0;
+}
+
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 e2264ad..9e2aa31 100644
--- a/xen/common/livepatch_elf.c
+++ b/xen/common/livepatch_elf.c
@@ -243,6 +243,7 @@ static int elf_get_sym(struct livepatch_elf *elf, const
void *data)
for ( i = 1; i < nsym; i++ )
{
const Elf_Sym *s = symtab_sec->data + symtab_sec->sec->sh_entsize * i;
+int rc;
delta = s->st_name;
/* Boundary check within the .strtab. */
@@ -255,6 +256,14 @@ static int elf_get_sym(struct livepatch_elf *elf, const
void *data)
sym[i].sym = s;
sym[i].name = strtab_sec->data + delta;
+/* On ARM we should NEVER see $t* symbols. */
+rc = arch_livepatch_symbol_check(elf, &sym[i]);
+if ( rc )
+{
+dprintk(XENLOG_ERR, LIVEPATCH "%s: Symbol '%s' should not be in
payload!\n",
+elf->name, sym[i].name);
+return rc;
+}
}
elf->nsym = nsym;
diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h
index c67b02c..edd905f 100644
--- a/xen/include/xen/livepatch.h
+++ b/xen/include/xen/livepatch.h
@@ -48,6 +48,8 @@ bool_t is_patch(const void *addr);
int arch_livepatch_verify_elf(const struct livepatch_elf *elf);
bool_t arch_livepatch_symbol_ok(const struct livepatch_elf *elf,
const struct livepatch_elf_sym *sym);
+int arch_livepatch_symbol_check(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);
--
2.4.11
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