Messages in this thread Patch in this message | | | From | Arnd Bergmann <> | Date | Wed, 30 Jun 2021 13:30:36 +0200 | Subject | Re: [RFC PATCH] cw1200: use kmalloc() allocation instead of stack |
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On Wed, Jun 30, 2021 at 11:56 AM Ulf Hansson <ulf.hansson@linaro.org> wrote: > > On Tue, 22 Jun 2021 at 22:33, Arnd Bergmann <arnd@arndb.de> wrote: > > > > On Tue, Jun 22, 2021 at 10:24 PM Jernej Skrabec > > <jernej.skrabec@gmail.com> wrote: > > > > > > It turns out that if CONFIG_VMAP_STACK is enabled and src or dst is > > > memory allocated on stack, SDIO operations fail due to invalid memory > > > address conversion: > > > > Thank you for sending this! > > > > It's worth pointing out that even without CONFIG_VMAP_STACK, using > > dma_map_sg() on a stack variable is broken, though it will appear to > > work most of the time but rarely cause a stack data corruption when > > the cache management goes wrong. > > > > This clearly needs to be fixed somewhere, if not with your patch, then > > a similar one. > > > > > diff --git a/drivers/net/wireless/st/cw1200/hwio.c b/drivers/net/wireless/st/cw1200/hwio.c > > > index 3ba462de8e91..5521cb7f2233 100644 > > > --- a/drivers/net/wireless/st/cw1200/hwio.c > > > +++ b/drivers/net/wireless/st/cw1200/hwio.c > > > @@ -66,33 +66,65 @@ static int __cw1200_reg_write(struct cw1200_common *priv, u16 addr, > > > static inline int __cw1200_reg_read_32(struct cw1200_common *priv, > > > u16 addr, u32 *val) > > > { > > > - __le32 tmp; > > > - int i = __cw1200_reg_read(priv, addr, &tmp, sizeof(tmp), 0); > > > - *val = le32_to_cpu(tmp); > > > + __le32 *tmp; > > > + int i; > > > + > > > + tmp = kmalloc(sizeof(*tmp), GFP_KERNEL); > > > + if (!tmp) > > > + return -ENOMEM; > > > + > > > + i = __cw1200_reg_read(priv, addr, tmp, sizeof(*tmp), 0); > > > + *val = le32_to_cpu(*tmp); > > > + kfree(tmp); > > > return i; > > > } > > > > There is a possible problem here when the function gets called from > > atomic context, so it might need to use GFP_ATOMIC instead of > > GFP_KERNEL. If it's never called from atomic context, then this patch > > looks correct to me. > > I would be surprised if this is called from atomic context (when IRQs > are turned off), because in most cases, to complete the read/write > request the mmc controller driver relies on IRQs being delivered.
I thought I had seen a spinlock in the forked driver, but I don't see it now, so I probably misremembered that bit.
> > The alternative would be to add a bounce buffer check based on > > is_vmalloc_or_module_addr() in sdio_io_rw_ext_helper(), which would > > add a small bit of complexity there but solve the problem for > > all drivers at once. In this case, it would probably have to use > > GFP_ATOMIC regardless of whether __cw1200_reg_read_32() > > is allowed to sleep, since other callers might not. > > I like the idea, but... > > I don't think we should see this as an alternative, but rather as a > complement which would have performance issues. A warning should be > printed, if the buffer isn't properly allocated.
Fair enough. I found the function call I was looking for: object_is_on_stack(), the patch below should print a warning once when a driver passes a bad buffer, but I did not test that.
There are some possible variations on that: an on-stack buffer by itself can work as long as the DMA is cache-coherent and stacks are not vmapped. For the is_vmalloc_or_module_addr() case, we may decide to just return an error, rather than running into a kernel oops.
> Additionally, I don't think GFT_ATOMIC should be needed.
Ok, I now see the mmc_wait_for_req() in mmc_io_rw_extended() that probably means it can not be called in atomic context at all, and that GFP_KERNEL is safe, and that any driver calling it with a spinlock held is already broken.
Arnd
8<--- diff --git a/drivers/mmc/core/sdio_ops.c b/drivers/mmc/core/sdio_ops.c index 4c229dd2b6e5..845f9ca3b200 100644 --- a/drivers/mmc/core/sdio_ops.c +++ b/drivers/mmc/core/sdio_ops.c @@ -124,6 +124,7 @@ int mmc_io_rw_extended(struct mmc_card *card, int write, unsigned fn, int err;
WARN_ON(blksz == 0); + WARN_ON_ONCE(is_vmalloc_or_module_addr(buf) || object_is_on_stack(buf));
/* sanity check */ if (addr & ~0x1FFFF)
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