Hi, On Thu, Oct 13, 2016 at 03:10:18PM +0200, Denys Vlasenko wrote: > On Fri, Sep 9, 2016 at 2:21 PM, Chen Yu <[email protected]> wrote: > > On some platforms, there is occasional panic triggered when trying to > > resume from hibernation, a typical panic looks like: > > > > "BUG: unable to handle kernel paging request at ffff880085894000 > > IP: [<ffffffff810c5dc2>] load_image_lzo+0x8c2/0xe70" > > > > Investigation carried out by Lee Chun-Yi show that this is because > > e820 map has been changed by BIOS across hibernation, and one > > of the page frames from suspend kernel is right located in restore > > kernel's unmapped region, so panic comes out when accessing unmapped > > kernel address. > > > > In order to expose this issue earlier, the md5 hash of e820 map > > is passed from suspend kernel to restore kernel, and the restore > > kernel will terminate the resume process once it finds the md5 > > hash are not the same. > > > > As the format of image header has been modified, the magic number > > should also be adjusted as kernels with the same RESTORE_MAGIC have > > to use the same header format and interpret all of the fields in > > it in the same way. > > > > If the suspend kernel is built without md5 support, and the restore > > kernel has md5 support, then the latter will bypass the check process. > > Vice versa the restore kernel will bypass the check if it does not > > support md5 operation. > > > > Note: > > 1. Without this patch applied, it is possible that BIOS has > > provided an inconsistent memory map, but the resume kernel is still > > able to restore the image anyway(e.g, E820_RAM region is the superset > > of the previous one), although the system might be unstable. So this > > patch tries to treat any inconsistent e820 as illegal. > > > > 2. Another case is, this patch replies on comparing the e820_saved, but > > currently the e820_save might not be strictly the same across > > hibernation, even if BIOS has provided consistent e820 map - In > > theory mptable might modify the BIOS-provided e820_saved dynamically > > in early_reserve_e820_mpc_new, which would allocate a buffer from > > E820_RAM, and marks it from E820_RAM to E820_RESERVED). > > This is a potential and rare case we need to deal with in OS in > > the future. > > > > Suggested-by: Pavel Machek <[email protected]> > > Suggested-by: Rafael J. Wysocki <[email protected]> > > Cc: Rafael J. Wysocki <[email protected]> > > Cc: Pavel Machek <[email protected]> > > Cc: Lee Chun-Yi <[email protected]> > > Cc: Borislav Petkov <[email protected]> > > Acked-by: Pavel Machek <[email protected]> > > Signed-off-by: Chen Yu <[email protected]> > > --- > > > +static int get_e820_md5(struct e820map *map, void *buf) > > +{ > > + struct scatterlist sg; > > + struct crypto_ahash *tfm; > > + struct ahash_request *req; > > + int ret = 0; > > + > > + tfm = crypto_alloc_ahash("md5", 0, CRYPTO_ALG_ASYNC); > > + if (IS_ERR(tfm)) > > + return -ENOMEM; > > + > > + req = ahash_request_alloc(tfm, GFP_KERNEL); > > + if (!req) { > > + ret = -ENOMEM; > > + goto free_ahash; > > + } > > I looked elsewhere in kernel, and there is this idiom for placing > struct ahash_request on stack. Instead of the ahash_request_alloc() > and never-actually-tirggering-error handling, you can do: > > { > AHASH_REQUEST_ON_STACK(req, tfm); > > > + > > + sg_init_one(&sg, (u8 *)map, sizeof(struct e820map)); > > + ahash_request_set_callback(req, 0, NULL, NULL); > > + ahash_request_set_crypt(req, &sg, buf, sizeof(struct e820map)); > > + > > + if (crypto_ahash_digest(req)) > > + ret = -EINVAL; > > + > > + ahash_request_free(req); > > + free_ahash: > > and, naturally, the free() and the label would not be needed too, > just close the one extra brace: > > > + crypto_free_ahash(tfm); > > + > > + return ret; > > } > > > +} OK, thanks for point it out, will do in next version.
Yu
