Date:	Sat, 5 Mar 2016 19:35:24 +0800
From:	Baoquan He <bhe@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	yinghai@...nel.org, keescook@...omium.org, hpa@...or.com,
	vgoyal@...hat.com, mingo@...hat.com, bp@...en8.de, luto@...nel.org,
	lasse.collin@...aani.org, akpm@...ux-foundation.org,
	dyoung@...hat.com
Subject: Re: [PATCH v3 00/19] x86, boot: kaslr cleanup and 64bit kaslr support

Forget mentioning this patchset is based on v4.5-rc6 of Linus's tree.

On 03/05/16 at 12:24am, Baoquan He wrote:
> ***Background:
> Previously a bug is reported that kdump didn't work when kaslr is enabled. During
> discussing that bug fix, we found current kaslr has a limilation that it can
> only randomize in 1GB region.
> 
> This is because in curent kaslr implementaion only physical address of kernel
> loading is randomized. Then calculate the delta of physical address where
> vmlinux was linked to load and where it is finally loaded. If delta is not
> equal to 0, namely there's a new physical address where kernel is actually
> decompressed, relocation handling need be done. Then delta is added to offset
> of kernel symbol relocation, this makes the address of kernel text mapping move
> delta long. Though in principle kernel can be randomized to any physical address,
> kernel text mapping address space is limited and only 1G, namely as follows on
> x86_64:
> 	[0xffffffff80000000, 0xffffffffc0000000)
> 
> In one word, kernel text physical address and virtual address randomization is
> coupled. This causes the limitation.
> 
> Then hpa and Vivek suggested we should change this. To decouple the physical
> address and virtual address randomization of kernel text and let them work
> separately. Then kernel text physical address can be randomized in region
> [16M, 64T), and kernel text virtual address can be randomized in region
> [0xffffffff80000000, 0xffffffffc0000000).
> 
> ***Problems we need solved:
>   - For kernel boot from startup_32 case, only 0~4G identity mapping is built.
>     If kernel will be randomly put anywhere from 16M to 64T at most, the price
>     to build all region of identity mapping is too high. We need build the
>     identity mapping on demand, not covering all physical address space.
> 
>   - Decouple the physical address and virtual address randomization of kernel
>     text and let them work separately.
> 
> ***Parts:
>    - The 1st part is Yinghai's identity mapping building on demand patches.
>      This is used to solve the first problem mentioned above.
>      (Patch 09-10/19)
>    - The 2nd part is decoupling the physical address and virtual address
>      randomization of kernel text and letting them work separately patches
>      based on Yinghai's ident mapping patches.
>      (Patch 12-19/19)
>    - The 3rd part is some clean up patches which Yinghai found when he reviewed
>      my patches and the related code around.
>      (Patch 01-08/19)
> 
> ***Patch status:
> This patchset went through several rounds of review.
> 
>    - The first round can be found here:
> 	https://lwn.net/Articles/637115/
> 
>    - In 2nd round Yinghai made a big patchset including this kaslr fix and another
>      setup_data related fix. The link is here:
>       http://lists-archives.com/linux-kernel/28346903-x86-updated-patches-for-kaslr-and-setup_data-etc-for-v4-3.html
>      You can get the code from Yinghai's git branch:
>      git://git.kernel.org/pub/scm/linux/kernel/git/yinghai/linux-yinghai.git for-x86-v4.3-next
> 
>    - This post is the 3rd round. It only takes care of the kaslr related patches.
>      For reviewers it's better to discuss only one issue in one thread.
>        * I take off one patch as follows from Yinghai's because I think it's unnecessay. 
>           - Patch 05/19 x86, kaslr: rename output_size to output_run_size
>          output_size is enough to represen the value:
> 		output_len > run_size ? output_len : run_size
>       
>        * I add Patch 04/19, it's a comment update patch. For other patches, I just
>          adjust patch log and do several places of change comparing with 2nd round.
>          Please check the change log under patch log of each patch for details.
> 
>        * I adjust sequence of several patches to make review easier. It doesn't
>          affect codes.
> 
>    - You can also get this patchset from my github:
>      https://github.com/baoquan-he/linux.git kaslr-above-4G
> 
> Any comments and suggestions are welcome. Code changes, code comments, patch logs,
> anything you think it's unclear, please add your comment.
> 
> Baoquan He (8):
>   x86, kaskr: Update the description for decompressor worst case
>   x86, kaslr: Fix a bug that relocation can not be handled when kernel
>     is loaded above 2G
>   x86, kaslr: Introduce struct slot_area to manage randomization slot
>     info
>   x86, kaslr: Add two functions which will be used later
>   x86, kaslr: Introduce fetch_random_virt_offset to randomize the kernel
>     text mapping address
>   x86, kaslr: Randomize physical and virtual address of kernel
>     separately
>   x86, kaslr: Add support of kernel physical address randomization above
>     4G
>   x86, kaslr: Remove useless codes
> 
> Yinghai Lu (11):
>   x86, kaslr: Remove not needed parameter for choose_kernel_location
>   x86, boot: Move compressed kernel to end of buffer before
>     decompressing
>   x86, boot: Move z_extract_offset calculation to header.S
>   x86, boot: Fix run_size calculation
>   x86, kaslr: Clean up useless code related to run_size.
>   x86, kaslr: Get correct max_addr for relocs pointer
>   x86, kaslr: Consolidate mem_avoid array filling
>   x86, boot: Split kernel_ident_mapping_init to another file
>   x86, 64bit: Set ident_mapping for kaslr
>   x86, boot: Add checking for memcpy
>   x86, kaslr: Allow random address to be below loaded address
> 
>  arch/x86/boot/Makefile                 |  13 +-
>  arch/x86/boot/compressed/Makefile      |  19 ++-
>  arch/x86/boot/compressed/aslr.c        | 258 +++++++++++++++++++++++----------
>  arch/x86/boot/compressed/head_32.S     |  14 +-
>  arch/x86/boot/compressed/head_64.S     |  15 +-
>  arch/x86/boot/compressed/misc.c        |  94 +++++++-----
>  arch/x86/boot/compressed/misc.h        |  34 +++--
>  arch/x86/boot/compressed/misc_pgt.c    |  91 ++++++++++++
>  arch/x86/boot/compressed/mkpiggy.c     |  28 +---
>  arch/x86/boot/compressed/string.c      |  29 +++-
>  arch/x86/boot/compressed/vmlinux.lds.S |   1 +
>  arch/x86/boot/header.S                 |  22 ++-
>  arch/x86/include/asm/boot.h            |  19 +++
>  arch/x86/include/asm/page.h            |   5 +
>  arch/x86/kernel/asm-offsets.c          |   1 +
>  arch/x86/kernel/vmlinux.lds.S          |   1 +
>  arch/x86/mm/ident_map.c                |  74 ++++++++++
>  arch/x86/mm/init_64.c                  |  74 +---------
>  arch/x86/tools/calc_run_size.sh        |  42 ------
>  19 files changed, 543 insertions(+), 291 deletions(-)
>  create mode 100644 arch/x86/boot/compressed/misc_pgt.c
>  create mode 100644 arch/x86/mm/ident_map.c
>  delete mode 100644 arch/x86/tools/calc_run_size.sh
> 
> -- 
> 2.5.0
> 

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