Re: [RFC PATCH] cw1200: use kmalloc() allocation instead of stack
From: Arnd Bergmann <arnd@arndb.de>
Date: 2021-06-22 20:33:22
Also in:
linux-wireless, lkml
On Tue, Jun 22, 2021 at 10:24 PM Jernej Skrabec [off-list ref] 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.
quoted hunk ↗ jump to hunk
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.
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.
Arnd