kselftest/arm64: Preserve any EXTRA_CONTEXT in handle_signal_copyctx()

When preserving the signal context for later verification by testcases
check for and include any EXTRA_CONTEXT block if enough space has been
provided.

Since the EXTRA_CONTEXT block includes a pointer to the start of the
additional data block we need to do at least some fixup on the copied
data. For simplicity in users we do this by extending the length of
the EXTRA_CONTEXT to include the following termination record, this
will cause users to see the extra data as part of the linked list of
contexts without needing any special handling. Care will be needed if
any specific tests for EXTRA_CONTEXT are added beyond the validation
done in ASSERT_GOOD_CONTEXT.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220829160703.874492-9-broonie@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

tools/testing/selftests/arm64/signal/test_signals_utils.c

@@ -168,15 +168,61 @@ static bool handle_signal_copyctx(struct tdescr *td,
 				  siginfo_t *si, void *uc_in)
 {
 	ucontext_t *uc = uc_in;
+	struct _aarch64_ctx *head;
+	struct extra_context *extra, *copied_extra;
+	size_t offset = 0;
+	size_t to_copy;
 
 	ASSERT_GOOD_CONTEXT(uc);
 
 	/* Mangling PC to avoid loops on original BRK instr */
 	uc->uc_mcontext.pc += 4;
-	memcpy(td->live_uc, uc, td->live_sz);
+
+	/*
+	 * Check for an preserve any extra data too with fixups.
+	 */
+	head = (struct _aarch64_ctx *)uc->uc_mcontext.__reserved;
+	head = get_header(head, EXTRA_MAGIC, td->live_sz, &offset);
+	if (head) {
+		extra = (struct extra_context *)head;
+
+		/*
+		 * The extra buffer must be immediately after the
+		 * extra_context and a 16 byte terminator. Include it
+		 * in the copy, this was previously validated in
+		 * ASSERT_GOOD_CONTEXT().
+		 */
+		to_copy = offset + sizeof(struct extra_context) + 16 +
+			extra->size;
+		copied_extra = (struct extra_context *)&(td->live_uc->uc_mcontext.__reserved[offset]);
+	} else {
+		copied_extra = NULL;
+		to_copy = sizeof(ucontext_t);
+	}
+
+	if (to_copy > td->live_sz) {
+		fprintf(stderr,
+			"Not enough space to grab context, %lu/%lu bytes\n",
+			td->live_sz, to_copy);
+		return false;
+	}
+
+	memcpy(td->live_uc, uc, to_copy);
+
+	/*
+	 * If there was any EXTRA_CONTEXT fix up the size to be the
+	 * struct extra_context and the following terminator record,
+	 * this means that the rest of the code does not need to have
+	 * special handling for the record and we don't need to fix up
+	 * datap for the new location.
+	 */
+	if (copied_extra)
+		copied_extra->head.size = sizeof(*copied_extra) + 16;
+
 	td->live_uc_valid = 1;
 	fprintf(stderr,
-		"GOOD CONTEXT grabbed from sig_copyctx handler\n");
+		"%lu byte GOOD CONTEXT grabbed from sig_copyctx handler\n",
+		to_copy);
 
 	return true;
 }