[Xen-devel] [PATCH v5 07/16] livepatch: ARM 32|64: Ignore mapping symbols: $[d, a, x]

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

Those symbols are used to help final linkers to replace insn.
The ARM ELF specification mandates that they are present
to denote the start of certain CPU features. There are two
variants of it - short and long format.

Either way - we can ignore these symbols.

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> [x86 bits]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

---
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

v1: First submission
v2: Update the order of symbols, fix title
    Add {} in after the first if - per Jan's recommendation.
v3: Add Andrew's Review tag
    Make the function return an bool_t.
    Skip check for '$t'
    Fix spelling of comments.
    s/arch_is_payload_symbol/arch_livepatch_symbol_ok/
v4: s/bool_t/bool/
v5: Removed an extra space in the conditional.
---
 xen/arch/arm/livepatch.c    | 33 +++++++++++++++++++++++++++++++++
 xen/arch/x86/livepatch.c    |  7 +++++++
 xen/common/livepatch.c      |  2 +-
 xen/include/xen/livepatch.h |  2 ++
 4 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/livepatch.c b/xen/arch/arm/livepatch.c
index 9284766..9959315 100644
--- a/xen/arch/arm/livepatch.c
+++ b/xen/arch/arm/livepatch.c
@@ -84,6 +84,39 @@ void arch_livepatch_unmask(void)
     local_abort_enable();
 }
 
+bool arch_livepatch_symbol_ok(const struct livepatch_elf *elf,
+                              const struct livepatch_elf_sym *sym)
+{
+    /*
+     * - Mapping symbols - denote the "start of a sequence of bytes of the
+     *   appropriate type" to mark certain features - such as start of region
+     *   containing data ($d); ARM ($a), or A64 ($x) instructions.
+     *   We ignore Thumb instructions ($t) as we shouldn't have them.
+     *
+     * The format is either short: '$x' or long: '$x.<any>'. We do not
+     * need this and more importantly - each payload will contain this
+     * resulting in symbol collisions.
+     */
+    if ( *sym->name == '$' && sym->name[1] != '\0' )
+    {
+        char p = sym->name[1];
+        size_t len = strlen(sym->name);
+
+        if ( (len >= 3 && (sym->name[2] == '.' )) || (len == 2) )
+        {
+            if ( p == 'd' ||
+#ifdef CONFIG_ARM_32
+                 p == 'a'
+#else
+                 p == 'x'
+#endif
+               )
+                return false;
+        }
+    }
+    return true;
+}
+
 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 b0d81d7..7a369a0 100644
--- a/xen/arch/x86/livepatch.c
+++ b/xen/arch/x86/livepatch.c
@@ -124,6 +124,13 @@ int arch_livepatch_verify_elf(const struct livepatch_elf 
*elf)
     return 0;
 }
 
+bool arch_livepatch_symbol_ok(const struct livepatch_elf *elf,
+                              const struct livepatch_elf_sym *sym)
+{
+    /* No special checks on x86. */
+    return true;
+}
+
 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.c b/xen/common/livepatch.c
index f2f866c..082f553 100644
--- a/xen/common/livepatch.c
+++ b/xen/common/livepatch.c
@@ -749,7 +749,7 @@ static bool_t is_payload_symbol(const struct livepatch_elf 
*elf,
          !strncmp(sym->name, ".L", 2) )
         return 0;
 
-    return 1;
+    return arch_livepatch_symbol_ok(elf, sym);
 }
 
 static int build_symbol_table(struct payload *payload,
diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h
index b7b84e7..e8c67d6 100644
--- a/xen/include/xen/livepatch.h
+++ b/xen/include/xen/livepatch.h
@@ -48,6 +48,8 @@ bool_t is_patch(const void *addr);
 
 /* Arch hooks. */
 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);
 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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