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    Subject[PATCH 4.9 42/46] drivers/misc/sgi-gru: fix Spectre v1 vulnerability
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

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

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

    commit fee05f455ceb5c670cbe48e2f9454ebc4a388554 upstream.

    req.gid can be indirectly 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:

    vers/misc/sgi-gru/grukdump.c:200 gru_dump_chiplet_request() warn:
    potential spectre issue 'gru_base' [w]

    Fix this by sanitizing req.gid before calling macro GID_TO_GRU, which
    uses it to index gru_base.

    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

    Cc: stable@vger.kernel.org
    Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/misc/sgi-gru/grukdump.c | 4 ++++
    1 file changed, 4 insertions(+)

    --- a/drivers/misc/sgi-gru/grukdump.c
    +++ b/drivers/misc/sgi-gru/grukdump.c
    @@ -27,6 +27,9 @@
    #include <linux/delay.h>
    #include <linux/bitops.h>
    #include <asm/uv/uv_hub.h>
    +
    +#include <linux/nospec.h>
    +
    #include "gru.h"
    #include "grutables.h"
    #include "gruhandles.h"
    @@ -196,6 +199,7 @@ int gru_dump_chiplet_request(unsigned lo
    /* Currently, only dump by gid is implemented */
    if (req.gid >= gru_max_gids)
    return -EINVAL;
    + req.gid = array_index_nospec(req.gid, gru_max_gids);

    gru = GID_TO_GRU(req.gid);
    ubuf = req.buf;

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