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    SubjectRe: [PATCH -v2] Audit: push audit success and retcode into arch ptrace.h
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    On Tue, 2011-06-07 at 19:19 +0200, Oleg Nesterov wrote:
    > On 06/03, Eric Paris wrote:
    > >
    > > The audit system previously expected arches calling to audit_syscall_exit to
    > > supply as arguments if the syscall was a success and what the return code was.
    > > Audit also provides a helper AUDITSC_RESULT which was supposed to simplify things
    > > by converting from negative retcodes to an audit internal magic value stating
    > > success or failure. This helper was wrong and could indicate that a valid
    > > pointer returned to userspace was a failed syscall. The fix is to fix the
    > > layering foolishness. We now pass audit_syscall_exit a struct pt_reg and it
    > > in turns calls back into arch code to collect the return value and to
    > > determine if the syscall was a success or failure. We also define a generic
    > > is_syscall_success() macro which determines success/failure based on if the
    > > value is < -MAX_ERRNO. This works for arches like x86 which do not use a
    > > separate mechanism to indicate syscall failure.
    >
    > I know nothing about audit, but the patch looks fine to me.
    >
    >
    > But I have a bit off-topic question,
    >
    > > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
    > > index 8a445a0..b7b1f88 100644
    > > --- a/arch/x86/kernel/entry_64.S
    > > +++ b/arch/x86/kernel/entry_64.S
    > > @@ -53,6 +53,7 @@
    > > #include <asm/paravirt.h>
    > > #include <asm/ftrace.h>
    > > #include <asm/percpu.h>
    > > +#include <linux/err.h>
    > >
    > > /* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this. */
    > > #include <linux/elf-em.h>
    > > @@ -564,17 +565,16 @@ auditsys:
    > > jmp system_call_fastpath
    > >
    > > /*
    > > - * Return fast path for syscall audit. Call audit_syscall_exit()
    > > + * Return fast path for syscall audit. Call __audit_syscall_exit()
    > > * directly and then jump back to the fast path with TIF_SYSCALL_AUDIT
    > > * masked off.
    > > */
    > > sysret_audit:
    > > movq RAX-ARGOFFSET(%rsp),%rsi /* second arg, syscall return value */
    > > - cmpq $0,%rsi /* is it < 0? */
    > > - setl %al /* 1 if so, 0 if not */
    > > + cmpq $-MAX_ERRNO,%rsi /* is it < -MAX_ERRNO? */
    > > + setbe %al /* 1 if so, 0 if not */
    > > movzbl %al,%edi /* zero-extend that into %edi */
    > > - inc %edi /* first arg, 0->1(AUDITSC_SUCCESS), 1->2(AUDITSC_FAILURE) */
    > > - call audit_syscall_exit
    > > + call __audit_syscall_exit
    >
    > With or without this patch, can't we call audit_syscall_exit() twice
    > if there is something else in _TIF_WORK_SYSCALL_EXIT mask apart from
    > SYSCALL_AUDIT ? First time it is called from asm, then from
    > syscall_trace_leave(), no?
    >
    > For example. The task has TIF_SYSCALL_AUDIT and nothing else, it does
    > system_call->auditsys->system_call_fastpath. What if it gets, say,
    > TIF_SYSCALL_TRACE before ret_from_sys_call?

    No harm is done calling twice. The first call will do the real work and
    cleanup. It will set a flag in the audit data that the work has been
    done (in_syscall == 0) thus the second call will then not do any real
    work and won't have anything to clean up.

    -Eric



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