Re: [PATCH v3 1/3] powerpc: Don't force ENOSYS as error on syscall fail

From: Purcareata Bogdan
Date: Wed Feb 18 2015 - 01:51:22 EST

On 18.02.2015 05:01, Mike Strosaker wrote:
This patch failed to build using pseries_le_defconfig. With the change
noted below in entry_64.S, the build succeeded and seccomp mode 2 worked

Mike Strosaker

On 02/13/2015 02:22 AM, Bogdan Purcareata wrote:
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

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

- 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
cmplwi 0,r0,NR_syscalls
lis r10,sys_call_table@h
ori r10,r10,sys_call_table@l
slwi r0,r0,2
bge- 66f
lwzx r10,r10,r0 /* Fetch system call handler [ptr] */
mtlr r10
@@ -457,6 +457,11 @@ syscall_dotrace:
lwz r7,GPR7(r1)
lwz r8,GPR8(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

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index d180caf2..0d22fa8 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
ld r10,TI_FLAGS(r11)
andi. r11,r10,_TIF_SYSCALL_DOTRACE
bne syscall_dotrace
cmpldi 0,r0,NR_syscalls
bge- syscall_enosys

@@ -253,7 +252,9 @@ syscall_dotrace:
ld r10,TI_FLAGS(r10)
- b .Lsyscall_dotrace_cont
+ cmpldi 0,r0,NR_syscalls
+ bge- syscall_exit

Shouldn't this be .Lsyscall_exit?

Thanks for testing and spotting this! The kernel I tested with didn't have syscall_exit converted to a local label (commit 4c3b21686111e0ac6018469dacbc5549f9915cf8).

Will resend with this change.

Bogdan P.

+ b system_call

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)

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]);

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