kselftest: arm64: fake_sigreturn_bad_size

Add a simple fake_sigreturn testcase which builds a ucontext_t with a
badly sized header that causes a overrun in the __reserved area and
place it onto the stack. Expects a SIGSEGV on test PASS.

Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_size.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_size.c
new file mode 100644 (file)
index 0000000..b3c3621
--- /dev/null
+++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_size.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 ARM Limited
+ *
+ * Place a fake sigframe on the stack including a bad record overflowing
+ * the __reserved space: on sigreturn Kernel must spot this attempt and
+ * the test case is expected to be terminated via SEGV.
+ */
+
+#include <signal.h>
+#include <ucontext.h>
+
+#include "test_signals_utils.h"
+#include "testcases.h"
+
+struct fake_sigframe sf;
+
+#define MIN_SZ_ALIGN   16
+
+static int fake_sigreturn_bad_size_run(struct tdescr *td,
+                                      siginfo_t *si, ucontext_t *uc)
+{
+       size_t resv_sz, need_sz, offset;
+       struct _aarch64_ctx *shead = GET_SF_RESV_HEAD(sf), *head;
+
+       /* just to fill the ucontext_t with something real */
+       if (!get_current_context(td, &sf.uc))
+               return 1;
+
+       resv_sz = GET_SF_RESV_SIZE(sf);
+       /* at least HDR_SZ + bad sized esr_context needed */
+       need_sz = sizeof(struct esr_context) + HDR_SZ;
+       head = get_starting_head(shead, need_sz, resv_sz, &offset);
+       if (!head)
+               return 0;
+
+       /*
+        * Use an esr_context to build a fake header with a
+        * size greater then the free __reserved area minus HDR_SZ;
+        * using ESR_MAGIC here since it is not checked for size nor
+        * is limited to one instance.
+        *
+        * At first inject an additional normal esr_context
+        */
+       head->magic = ESR_MAGIC;
+       head->size = sizeof(struct esr_context);
+       /* and terminate properly */
+       write_terminator_record(GET_RESV_NEXT_HEAD(head));
+       ASSERT_GOOD_CONTEXT(&sf.uc);
+
+       /*
+        * now mess with fake esr_context size: leaving less space than
+        * needed while keeping size value 16-aligned
+        *
+        * It must trigger a SEGV from Kernel on:
+        *
+        *      resv_sz - offset < sizeof(*head)
+        */
+       /* at first set the maximum good 16-aligned size */
+       head->size = (resv_sz - offset - need_sz + MIN_SZ_ALIGN) & ~0xfUL;
+       /* plus a bit more of 16-aligned sized stuff */
+       head->size += MIN_SZ_ALIGN;
+       /* and terminate properly */
+       write_terminator_record(GET_RESV_NEXT_HEAD(head));
+       ASSERT_BAD_CONTEXT(&sf.uc);
+       fake_sigreturn(&sf, sizeof(sf), 0);
+
+       return 1;
+}
+
+struct tdescr tde = {
+               .name = "FAKE_SIGRETURN_BAD_SIZE",
+               .descr = "Triggers a sigreturn with a overrun __reserved area",
+               .sig_ok = SIGSEGV,
+               .timeout = 3,
+               .run = fake_sigreturn_bad_size_run,
+};