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arm64: ptrace: allow tracer to skip a system call

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If tracer modifies a syscall number to -1, this traced system call should
be skipped with a return value specified in x0.
This patch implements this semantics.

Please note:
* syscall entry tracing and syscall exit tracing (ftrace tracepoint and
  audit) are always executed, if enabled, even when skipping a system call
  (that is, -1).
  In this way, we can avoid a potential bug where audit_syscall_entry()
  might be called without audit_syscall_exit() at the previous system call
  being called, that would cause OOPs in audit_syscall_entry().

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
[will: fixed up conflict with blr rework]
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
AKASHI Takahiro 2014-11-28 05:26:35 +00:00 committed by Will Deacon
parent 766a85d7bc
commit 1014c81d9a
1 changed files with 10 additions and 2 deletions
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12
arch/arm64/kernel/entry.S
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@ -669,8 +669,15 @@ ENDPROC(el0_svc)
* switches, and waiting for our parent to respond.
*/
__sys_trace:
mov x0, sp
mov w0, #-1 // set default errno for
cmp scno, x0 // user-issued syscall(-1)
b.ne 1f
mov x0, #-ENOSYS
str x0, [sp, #S_X0]
1: mov x0, sp
bl syscall_trace_enter
cmp w0, #-1 // skip the syscall?
b.eq __sys_trace_return_skipped
uxtw scno, w0 // syscall number (possibly new)
mov x1, sp // pointer to regs
cmp scno, sc_nr // check upper syscall limit
@ -683,7 +690,8 @@ __sys_trace:
blr x16 // call sys_* routine
__sys_trace_return:
str x0, [sp] // save returned x0
str x0, [sp, #S_X0] // save returned x0
__sys_trace_return_skipped:
mov x0, sp
bl syscall_trace_exit
b ret_to_user