lkml.org 
[lkml]   [2015]   [Aug]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v6 3/6] task_isolation: support PR_TASK_ISOLATION_STRICT mode
    Hi Chris,

    On Tue, Aug 25, 2015 at 08:55:52PM +0100, Chris Metcalf wrote:
    > With task_isolation mode, the task is in principle guaranteed not to
    > be interrupted by the kernel, but only if it behaves. In particular,
    > if it enters the kernel via system call, page fault, or any of a
    > number of other synchronous traps, it may be unexpectedly exposed
    > to long latencies. Add a simple flag that puts the process into
    > a state where any such kernel entry is fatal.
    >
    > To allow the state to be entered and exited, we ignore the prctl()
    > syscall so that we can clear the bit again later, and we ignore
    > exit/exit_group to allow exiting the task without a pointless signal
    > killing you as you try to do so.
    >
    > This change adds the syscall-detection hooks only for x86, arm64,
    > and tile.
    >
    > The signature of context_tracking_exit() changes to report whether
    > we, in fact, are exiting back to user space, so that we can track
    > user exceptions properly separately from other kernel entries.
    >
    > Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
    > ---
    > arch/arm64/kernel/ptrace.c | 5 +++++
    > arch/tile/kernel/ptrace.c | 5 ++++-
    > arch/x86/kernel/ptrace.c | 2 ++
    > include/linux/context_tracking.h | 11 ++++++++---
    > include/linux/isolation.h | 16 ++++++++++++++++
    > include/uapi/linux/prctl.h | 1 +
    > kernel/context_tracking.c | 9 ++++++---
    > kernel/isolation.c | 38 ++++++++++++++++++++++++++++++++++++++
    > 8 files changed, 80 insertions(+), 7 deletions(-)
    >
    > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
    > index d882b833dbdb..e3d83a12f3cf 100644
    > --- a/arch/arm64/kernel/ptrace.c
    > +++ b/arch/arm64/kernel/ptrace.c
    > @@ -37,6 +37,7 @@
    > #include <linux/regset.h>
    > #include <linux/tracehook.h>
    > #include <linux/elf.h>
    > +#include <linux/isolation.h>
    >
    > #include <asm/compat.h>
    > #include <asm/debug-monitors.h>
    > @@ -1150,6 +1151,10 @@ static void tracehook_report_syscall(struct pt_regs *regs,
    >
    > asmlinkage int syscall_trace_enter(struct pt_regs *regs)
    > {
    > + /* Ensure we report task_isolation violations in all circumstances. */
    > + if (test_thread_flag(TIF_NOHZ) && task_isolation_strict())

    This is going to force us to check TIF_NOHZ on the syscall slowpath even
    when CONFIG_TASK_ISOLATION=n.

    > + task_isolation_syscall(regs->syscallno);
    > +
    > /* Do the secure computing check first; failures should be fast. */

    Here we have the usual priority problems with all the subsystems that
    hook into the syscall path. If a prctl is later rewritten to a different
    syscall, do you care about catching it? Either way, the comment about
    doing secure computing "first" needs fixing.

    Cheers,

    Will


    \
     
     \ /
      Last update: 2015-08-26 12:41    [W:4.381 / U:0.420 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site