Messages in this thread | | | From | Denys Vlasenko <> | Date | Thu, 13 Oct 2016 15:10:18 +0200 | Subject | Re: [PATCH][v10] PM / hibernate: Verify the consistent of e820 memory map by md5 digest |
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On Fri, Sep 9, 2016 at 2:21 PM, Chen Yu <yu.c.chen@intel.com> 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 <pavel@ucw.cz> > Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Cc: Pavel Machek <pavel@ucw.cz> > Cc: Lee Chun-Yi <jlee@suse.com> > Cc: Borislav Petkov <bp@alien8.de> > Acked-by: Pavel Machek <pavel@ucw.cz> > Signed-off-by: Chen Yu <yu.c.chen@intel.com> > ---
> +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;
}
> +}
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