[PATCH v4 1/3] powerpc: Don't force ENOSYS as error on syscall fail

[Bogdan Purcareata]

In certain scenarios - e.g. seccomp filtering with ERRNO as default action -
the system call fails for other reasons than the syscall not being available.
The seccomp filter can be configured to store a user-defined error code on
return from a blacklisted syscall. Don't always set ENOSYS on
do_syscall_trace_enter failure.

Delegate setting ENOSYS in case of failure, where appropriate, to
do_syscall_trace_enter.

v4:
- update syscall_exit to be local label on 64bit, after rebasing on top of 3.19

v3:
- keep setting ENOSYS in the syscall entry assembly for scenarios without
  syscall tracing

v2:
- move setting ENOSYS as errno from the syscall entry assembly to
  do_syscall_trace_enter, only in the specific case

Signed-off-by: Bogdan Purcareata <bogdan.purcareata@xxxxxxxxxxxxx>
---
 arch/powerpc/kernel/entry_32.S | 7 ++++++-
 arch/powerpc/kernel/entry_64.S | 5 +++--
 arch/powerpc/kernel/ptrace.c   | 4 +++-
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 46fc0f4..b2f88cd 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -333,12 +333,12 @@ _GLOBAL(DoSyscall)
 	lwz	r11,TI_FLAGS(r10)
 	andi.	r11,r11,_TIF_SYSCALL_DOTRACE
 	bne-	syscall_dotrace
-syscall_dotrace_cont:
 	cmplwi	0,r0,NR_syscalls
 	lis	r10,sys_call_table@h
 	ori	r10,r10,sys_call_table@l
 	slwi	r0,r0,2
 	bge-	66f
+syscall_dotrace_cont:
 	lwzx	r10,r10,r0	/* Fetch system call handler [ptr] */
 	mtlr	r10
 	addi	r9,r1,STACK_FRAME_OVERHEAD
@@ -457,6 +457,11 @@ syscall_dotrace:
 	lwz	r7,GPR7(r1)
 	lwz	r8,GPR8(r1)
 	REST_NVGPRS(r1)
+	cmplwi	0,r0,NR_syscalls
+	lis	r10,sys_call_table@h
+	ori	r10,r10,sys_call_table@l
+	slwi	r0,r0,2
+	bge-	ret_from_syscall
 	b	syscall_dotrace_cont
 
 syscall_exit_work:
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index d180caf2..5e7434e 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -144,7 +144,6 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_SPLPAR)
 	ld	r10,TI_FLAGS(r11)
 	andi.	r11,r10,_TIF_SYSCALL_DOTRACE
 	bne	syscall_dotrace
-.Lsyscall_dotrace_cont:
 	cmpldi	0,r0,NR_syscalls
 	bge-	syscall_enosys
 
@@ -253,7 +252,9 @@ syscall_dotrace:
 	addi	r9,r1,STACK_FRAME_OVERHEAD
 	CURRENT_THREAD_INFO(r10, r1)
 	ld	r10,TI_FLAGS(r10)
-	b	.Lsyscall_dotrace_cont
+	cmpldi	0,r0,NR_syscalls
+	bge-	.Lsyscall_exit
+	b	system_call
 
 syscall_enosys:
 	li	r3,-ENOSYS
diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index f21897b..2edae06 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -1775,13 +1775,15 @@ long do_syscall_trace_enter(struct pt_regs *regs)
 	secure_computing_strict(regs->gpr[0]);
 
 	if (test_thread_flag(TIF_SYSCALL_TRACE) &&
-	    tracehook_report_syscall_entry(regs))
+	    tracehook_report_syscall_entry(regs)) {
 		/*
 		 * Tracing decided this syscall should not happen.
 		 * We'll return a bogus call number to get an ENOSYS
 		 * error, but leave the original number in regs->gpr[0].
 		 */
 		ret = -1L;
+		syscall_set_return_value(current, regs, ENOSYS, 0);
+	}
 
 	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 		trace_sys_enter(regs, regs->gpr[0]);
-- 
2.1.4

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