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    SubjectRe: [PATCH -v2] Audit: push audit success and retcode into arch ptrace.h
    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?

    Oleg.



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