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    Subject[PATCH 4.4 014/268] kernel/sys.c: fix potential Spectre v1 issue
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Gustavo A. R. Silva <gustavo@embeddedor.com>

    commit 23d6aef74da86a33fa6bb75f79565e0a16ee97c2 upstream.

    `resource' can be controlled by user-space, hence leading to a potential
    exploitation of the Spectre variant 1 vulnerability.

    This issue was detected with the help of Smatch:

    kernel/sys.c:1474 __do_compat_sys_old_getrlimit() warn: potential spectre issue 'get_current()->signal->rlim' (local cap)
    kernel/sys.c:1455 __do_sys_old_getrlimit() warn: potential spectre issue 'get_current()->signal->rlim' (local cap)

    Fix this by sanitizing *resource* before using it to index
    current->signal->rlim

    Notice that given that speculation windows are large, the policy is to
    kill the speculation on the first load and not worry if it can be
    completed with a dependent load/store [1].

    [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

    Link: http://lkml.kernel.org/r/20180515030038.GA11822@embeddedor.com
    Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
    Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
    Cc: Alexei Starovoitov <ast@kernel.org>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/sys.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/kernel/sys.c
    +++ b/kernel/sys.c
    @@ -53,6 +53,8 @@
    #include <linux/uidgid.h>
    #include <linux/cred.h>

    +#include <linux/nospec.h>
    +
    #include <linux/kmsg_dump.h>
    /* Move somewhere else to avoid recompiling? */
    #include <generated/utsrelease.h>
    @@ -1311,6 +1313,7 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned
    if (resource >= RLIM_NLIMITS)
    return -EINVAL;

    + resource = array_index_nospec(resource, RLIM_NLIMITS);
    task_lock(current->group_leader);
    x = current->signal->rlim[resource];
    task_unlock(current->group_leader);

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