sigreturn: Exercise the double-fault (bad iret) paths

1 files changed, 44 insertions, 2 deletions

diff --git a/sigreturn.c b/sigreturn.c
index 24dac43..bc111ab 100644
--- a/sigreturn.c
+++ b/sigreturn.c
@@ -35,6 +35,16 @@ static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
 		err(1, "sigaction");
 }
 
+static void clearhandler(int sig)
+{
+	struct sigaction sa;
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = SIG_DFL;
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(sig, &sa, 0))
+		err(1, "sigaction");
+}
+
 static unsigned char stack16[65536] __attribute__((aligned(4096)));
 
 asm (".pushsection .text\n\t"
@@ -87,7 +97,8 @@ static void setup_ldt(void)
 
 static gregset_t initial_regs, requested_regs, resulting_regs;
 
-static unsigned short sig_cs, sig_ss;
+static volatile unsigned short sig_cs, sig_ss;
+static volatile bool sig_trapped;
 
 #ifdef __x86_64__
 # define REG_IP REG_RIP
@@ -151,7 +162,7 @@ static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
 	asm ("mov %%ss,%0" : "=r" (ss));
 
 	greg_t asm_ss = ctx->uc_mcontext.gregs[REG_AX];
-	if (asm_ss != sig_ss) {
+	if (asm_ss != sig_ss && sig == SIGTRAP) {
 		printf("[FAIL]\tSIGTRAP: ss = %hx, frame ss = %hx, ax = %llx\n",
 		       ss, *ssptr(ctx), (unsigned long long)asm_ss);
 		nerrs++;
@@ -159,6 +170,8 @@ static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
 
 	memcpy(&resulting_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
 	memcpy(&ctx->uc_mcontext.gregs, &initial_regs, sizeof(gregset_t));
+
+	sig_trapped = true;
 }
 
 static char altstack_data[SIGSTKSZ];
@@ -290,6 +303,29 @@ static int do_test(int cs_bits, bool use_16bit_ss)
 	return nerrs;
 }
 
+static int test_bad_iret(int cs_bits)
+{
+	int cs = find_cs(cs_bits);
+	if (cs == -1)
+		return 0;
+
+	sig_cs = cs;
+	sig_ss = (2 << 3) | 7;
+
+	printf("[RUN]\t%d-bit CS (%hx), bogus SS (%hx)\n",
+	       cs_bits, sig_cs, sig_ss);
+
+	sig_trapped = false;
+	raise(SIGUSR1);
+	if (sig_trapped) {
+		printf("[OK]\tGot SIGSEGV\n");
+		return 0;
+	} else {
+		printf("[FAIL]\tDid not get SIGSEGV\n");
+		return 1;
+	}
+}
+
 int main()
 {
 	int total_nerrs = 0;
@@ -313,5 +349,11 @@ int main()
 	total_nerrs += do_test(32, true);
 	total_nerrs += do_test(16, true);
 
+	clearhandler(SIGTRAP);
+	sethandler(SIGSEGV, sigtrap, SA_ONSTACK);
+
+	test_bad_iret(64);
+	test_bad_iret(32);
+
 	return total_nerrs ? 1 : 0;
 }