lkml.org 
[lkml]   [2021]   [Oct]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 5.14 026/169] dma-debug: fix sg checks in debug_dma_map_sg()
    Date
    From: Gerald Schaefer <gerald.schaefer@linux.ibm.com>

    [ Upstream commit 293d92cbbd2418ca2ba43fed07f1b92e884d1c77 ]

    The following warning occurred sporadically on s390:
    DMA-API: nvme 0006:00:00.0: device driver maps memory from kernel text or rodata [addr=0000000048cc5e2f] [len=131072]
    WARNING: CPU: 4 PID: 825 at kernel/dma/debug.c:1083 check_for_illegal_area+0xa8/0x138

    It is a false-positive warning, due to broken logic in debug_dma_map_sg().
    check_for_illegal_area() checks for overlay of sg elements with kernel text
    or rodata. It is called with sg_dma_len(s) instead of s->length as
    parameter. After the call to ->map_sg(), sg_dma_len() will contain the
    length of possibly combined sg elements in the DMA address space, and not
    the individual sg element length, which would be s->length.

    The check will then use the physical start address of an sg element, and
    add the DMA length for the overlap check, which could result in the false
    warning, because the DMA length can be larger than the actual single sg
    element length.

    In addition, the call to check_for_illegal_area() happens in the iteration
    over mapped_ents, which will not include all individual sg elements if
    any of them were combined in ->map_sg().

    Fix this by using s->length instead of sg_dma_len(s). Also put the call to
    check_for_illegal_area() in a separate loop, iterating over all the
    individual sg elements ("nents" instead of "mapped_ents").

    While at it, as suggested by Robin Murphy, also move check_for_stack()
    inside the new loop, as it is similarly concerned with validating the
    individual sg elements.

    Link: https://lore.kernel.org/lkml/20210705185252.4074653-1-gerald.schaefer@linux.ibm.com
    Fixes: 884d05970bfb ("dma-debug: use sg_dma_len accessor")
    Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
    Signed-off-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/dma/debug.c | 12 ++++++------
    1 file changed, 6 insertions(+), 6 deletions(-)

    diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
    index 70519f67556f..fad3c77c1da1 100644
    --- a/kernel/dma/debug.c
    +++ b/kernel/dma/debug.c
    @@ -1299,6 +1299,12 @@ void debug_dma_map_sg(struct device *dev, struct scatterlist *sg,
    if (unlikely(dma_debug_disabled()))
    return;

    + for_each_sg(sg, s, nents, i) {
    + check_for_stack(dev, sg_page(s), s->offset);
    + if (!PageHighMem(sg_page(s)))
    + check_for_illegal_area(dev, sg_virt(s), s->length);
    + }
    +
    for_each_sg(sg, s, mapped_ents, i) {
    entry = dma_entry_alloc();
    if (!entry)
    @@ -1314,12 +1320,6 @@ void debug_dma_map_sg(struct device *dev, struct scatterlist *sg,
    entry->sg_call_ents = nents;
    entry->sg_mapped_ents = mapped_ents;

    - check_for_stack(dev, sg_page(s), s->offset);
    -
    - if (!PageHighMem(sg_page(s))) {
    - check_for_illegal_area(dev, sg_virt(s), sg_dma_len(s));
    - }
    -
    check_sg_segment(dev, s);

    add_dma_entry(entry);
    --
    2.33.0


    \
     
     \ /
      Last update: 2021-10-25 22:10    [W:4.055 / U:0.212 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site