[PATCH v2 2/2] selftests/seccomp: add sparc64 support

[Stian Halseth <stian@itx.no>]

sparc64 now selects HAVE_ARCH_SECCOMP_FILTER, so teach seccomp_bpf
how to read and write its registers: the syscall number lives in %g1
and the return value in %o0.  The NT_PRSTATUS regset appends the
register window read back from the tracee's stack and has no exported
layout, so use the sparc-specific PTRACE_GETREGS64/PTRACE_SETREGS64
requests instead, which transfer the uapi struct pt_regs directly.

Errors are signaled by the carry bit in tstate with a positive errno
value in %o0, so provide a SYSCALL_RET_SET that maintains both, and
mark the arch SYSCALL_RET_SET_ON_PTRACE_EXIT since a return value
poked at entry would be overwritten by the syscall skip path, as on
powerpc.

Passes 95 of 95 on an UltraSPARC T4-1 (16 skipped for missing
optional features such as uprobes).

Link: https://github.com/sparclinux/issues/issues/11
Signed-off-by: Stian Halseth <stian@itx.no>
---
v2: use PTRACE_GETREGS64/PTRACE_SETREGS64 and the uapi struct pt_regs
    instead of a locally defined NT_PRSTATUS regset layout, as
    suggested by Kees Cook. Note the historical %g0 omission in that
    layout, which shifts the u_regs indices by one.

 tools/testing/selftests/seccomp/seccomp_bpf.c | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 0622bc2acad4..3711060c22a7 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -1872,6 +1872,34 @@ TEST_F(TRACE_poke, getpid_runs_normally)
 # define ARCH_REGS		struct user_regs_struct
 # define SYSCALL_NUM(_regs)	(_regs).orig_d0
 # define SYSCALL_RET(_regs)	(_regs).d0
+#elif defined(__sparc__) && defined(__arch64__)
+# include <asm/ptrace.h>
+/*
+ * PTRACE_GETREGS64/PTRACE_SETREGS64 transfer the uapi struct pt_regs,
+ * but in the historical layout that omits %g0: the blob starts at %g1,
+ * so every u_regs index is one lower than the register number suggests.
+ */
+# define ARCH_REGS		struct pt_regs
+# define SYSCALL_NUM(_regs)	(_regs).u_regs[0]	/* %g1 */
+# define SYSCALL_RET(_regs)	(_regs).u_regs[7]	/* %o0 */
+/*
+ * A syscall error is signaled by the carry bit in tstate, with the
+ * errno held in %o0 as a positive value; the carry can only be
+ * written reliably once the syscall has been skipped or has run.
+ */
+# define SPARC64_TSTATE_CARRY	0x0000001100000000UL	/* xcc.c | icc.c */
+# define SYSCALL_RET_SET(_regs, _val)				\
+	do {							\
+		typeof(_val) _result = (_val);			\
+		if (_result < 0) {				\
+			SYSCALL_RET(_regs) = -_result;		\
+			(_regs).tstate |= SPARC64_TSTATE_CARRY;	\
+		} else {					\
+			SYSCALL_RET(_regs) = _result;		\
+			(_regs).tstate &= ~SPARC64_TSTATE_CARRY; \
+		}						\
+	} while (0)
+# define SYSCALL_RET_SET_ON_PTRACE_EXIT
 #else
 # error "Do not know how to find your architecture's registers and syscalls"
 #endif
@@ -1939,6 +1967,14 @@ const bool ptrace_entry_set_syscall_ret =
 #if defined(__x86_64__) || defined(__i386__) || defined(__mips__) || defined(__mc68000__)
 # define ARCH_GETREGS(_regs)	ptrace(PTRACE_GETREGS, tracee, 0, &(_regs))
 # define ARCH_SETREGS(_regs)	ptrace(PTRACE_SETREGS, tracee, 0, &(_regs))
+#elif defined(__sparc__) && defined(__arch64__)
+/*
+ * The NT_PRSTATUS regset appends the register window, which struct
+ * pt_regs does not carry; the sparc-specific requests transfer
+ * struct pt_regs directly (and take the buffer in addr).
+ */
+# define ARCH_GETREGS(_regs)	ptrace(PTRACE_GETREGS64, tracee, &(_regs), 0)
+# define ARCH_SETREGS(_regs)	ptrace(PTRACE_SETREGS64, tracee, &(_regs), 0)
 #else
 # define ARCH_GETREGS(_regs)	({					\
 		struct iovec __v;					\
-- 
2.43.0