Simon Horman <horms at verge.net.au> writes: > On Tue, Sep 16, 2008 at 03:18:23PM -0400, Jonathan Steel wrote: >> A segmentation fault can occur in kimage_add_entry in kexec.c when >> loading a kernel image into memory. The fault occurs because a page is >> requested by calling kimage_alloc_page with gfp_mask GFP_KERNEL and the >> function may actually return a page with gfp_mask GFP_HIGHUSER. The high >> mem page is returned because it was swapped with the kernel page due to >> the kernel page being a page that will shortly be copied to. >> >> This patch ensures that kimage_alloc_page returns a page that was >> created with the correct gfp flags. > > I wonder if this problem might also affect other users of > kimage_alloc_pages(), and if so, perhaps it should guard > against this? No. kimage_alloc_pages() is a light wrapper around alloc_pages that simply marks the pages as reserved so they don't get used for other things while we have a hold of them. kimage_alloc_page() does a check to see if the page we have just allocated is the a page we are going to copy to and if so it does the copy of the data now, and frees the page that was holding the data. As an optimization it returns the page holding the data. The problem is that we allocate control pages as GFP_KERNEL and data pages GFP_HIGHUSER. And so they are not completely interchangeable. Since this check and swap only happens inside of kimage_alloc_page it only affects kimage_alloc_page. Eric n
