[PATCH 11/15] selftests/seccomp: Remove SYSCALL_NUM_RET_SHARE_REG in favor of SYSCALL_RET_SET

Kees Cook
2020-09-12T11:10:35Z

Instead of special-casing the specific case of shared registers, create
a default SYSCALL_RET_SET() macro (mirroring SYSCALL_NUM_SET()), that
writes to the SYSCALL_RET register. For architectures that can't set the
return value (for whatever reason), they can define SYSCALL_RET_SET()
without an associated SYSCALL_RET() macro. This also paves the way for
architectures that need to do special things to set the return value
(e.g. powerpc).

Signed-off-by: Kees Cook <keescook@chromium.org>
---
tools/testing/selftests/seccomp/seccomp_bpf.c | 33 +++++++++++++------
1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 2790d9cd50f4..623953a53032 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -1753,8 +1753,8 @@ TEST_F(TRACE_poke, getpid_runs_normally)
#elif defined(__s390__)
# define ARCH_REGS s390_regs
# define SYSCALL_NUM(_regs) (_regs).gprs[2]
-# define SYSCALL_RET(_regs) (_regs).gprs[2]
-# define SYSCALL_NUM_RET_SHARE_REG
+# define SYSCALL_RET_SET(_regs, _val) \
+ TH_LOG("Can't modify syscall return on this architecture")
#elif defined(__mips__)
# include <asm/unistd_nr_n32.h>
# include <asm/unistd_nr_n64.h>
@@ -1776,8 +1776,8 @@ TEST_F(TRACE_poke, getpid_runs_normally)
else \
(_regs).regs[2] = _nr; \
} while (0)
-# define SYSCALL_RET(_regs) (_regs).regs[2]
-# define SYSCALL_NUM_RET_SHARE_REG
+# define SYSCALL_RET_SET(_regs, _val) \
+ TH_LOG("Can't modify syscall return on this architecture")
#elif defined(__xtensa__)
# define ARCH_REGS struct user_pt_regs
# define SYSCALL_NUM(_regs) (_regs).syscall
@@ -1804,9 +1804,26 @@ TEST_F(TRACE_poke, getpid_runs_normally)
SYSCALL_NUM(_regs) = (_nr); \
} while (0)
#endif
+/*
+ * Most architectures can change the syscall return value by just
+ * writing to the SYSCALL_RET register. This is the default if not
+ * defined above. If an architecture cannot set the return value
+ * (for example when the syscall and return value register is
+ * shared), report it with TH_LOG() in an arch-specific definition
+ * of SYSCALL_RET_SET() above, and leave SYSCALL_RET undefined.
+ */
+#if !defined(SYSCALL_RET) && !defined(SYSCALL_RET_SET)
+# error "One of SYSCALL_RET or SYSCALL_RET_SET is needed for this arch"
+#endif
+#ifndef SYSCALL_RET_SET
+# define SYSCALL_RET_SET(_regs, _val) \
+ do { \
+ SYSCALL_RET(_regs) = (_val); \
+ } while (0)
+#endif

/* When the syscall return can't be changed, stub out the tests for it. */
-#ifdef SYSCALL_NUM_RET_SHARE_REG
+#ifndef SYSCALL_RET
# define EXPECT_SYSCALL_RETURN(val, action) EXPECT_EQ(-1, action)
#else
# define EXPECT_SYSCALL_RETURN(val, action) \
@@ -1870,11 +1887,7 @@ void change_syscall(struct __test_metadata *_metadata,

/* If syscall is skipped, change return value. */
if (syscall == -1)
-#ifdef SYSCALL_NUM_RET_SHARE_REG
- TH_LOG("Can't modify syscall return on this architecture");
-#else
- SYSCALL_RET(regs) = result;
-#endif
+ SYSCALL_RET_SET(regs, result);

/* Flush any register changes made. */
if (memcmp(&orig, &regs, sizeof(orig)) != 0)
--
2.25.1