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Date: Tue, 06 Oct 2020 21:12:14 -0700 (PDT)
From: Palmer Dabbelt <palmerdabbelt@...gle.com>
To: guoren@...nel.org
CC: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
guoren@...ux.alibaba.com, atishp@...shpatra.org,
schwab@...ux-m68k.org
Subject: Re: [PATCH] riscv: Fixup bootup failure with HARDENED_USERCOPY
On Tue, 06 Oct 2020 09:49:33 PDT (-0700), guoren@...nel.org wrote:
> From: Guo Ren <guoren@...ux.alibaba.com>
>
> As Aurelien has reported:
>
> [ 3.484586] AppArmor: AppArmor sha1 policy hashing enabled
> [ 4.749835] Freeing unused kernel memory: 492K
> [ 4.752017] Run /init as init process
> [ 4.753571] usercopy: Kernel memory overwrite attempt detected to kernel text (offset 507879, size 11)!
> [ 4.754838] ------------[ cut here ]------------
> [ 4.755651] kernel BUG at mm/usercopy.c:99!
> [ 4.756445] Kernel BUG [#1]
> [ 4.756815] Modules linked in:
> [ 4.757542] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.8.0-1-riscv64 #1 Debian 5.8.7-1
> [ 4.758372] epc: ffffffe0003b5120 ra : ffffffe0003b5120 sp : ffffffe07f783ca0
> [ 4.758960] gp : ffffffe000cc7230 tp : ffffffe07f77cec0 t0 : ffffffe000cdafc0
> [ 4.759772] t1 : 0000000000000064 t2 : 0000000000000000 s0 : ffffffe07f783cf0
> [ 4.760534] s1 : ffffffe00095d780 a0 : 000000000000005b a1 : 0000000000000020
> [ 4.761309] a2 : 0000000000000005 a3 : 0000000000000000 a4 : ffffffe000c1f340
> [ 4.761848] a5 : ffffffe000c1f340 a6 : 0000000000000000 a7 : 0000000000000087
> [ 4.762684] s2 : ffffffe000941848 s3 : 000000000007bfe7 s4 : 000000000000000b
> [ 4.763500] s5 : 0000000000000000 s6 : ffffffe00091cc00 s7 : fffffffffffff000
> [ 4.764376] s8 : 0000003ffffff000 s9 : ffffffe0769f3200 s10: 000000000000000b
> [ 4.765208] s11: ffffffe07d548c40 t3 : 0000000000000000 t4 : 000000000001dcd0
> [ 4.766059] t5 : ffffffe000cc8510 t6 : ffffffe000cd64aa
> [ 4.766712] status: 0000000000000120 badaddr: 0000000000000000 cause: 0000000000000003
> [ 4.768308] ---[ end trace 1f8e733e834d4c3e ]---
> [ 4.769129] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
> [ 4.770070] SMP: stopping secondary CPUs
> [ 4.771110] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---
>
> Above failure is relate to commit: a0fa4027dc911 (riscv: Fixup
That commit isn't in Linus' tree (at least, as far as I see it). I have
6184358da000 ("riscv: Fixup static_obj() fail"), so I'm going to fix that -- in
fact, I'm going to essentially just replace most of this rationale with what I
wrote up in my revert as this is all a bit too long for a commit message.
I was kind of worried the initdata move was a bit too risky, but after reading
the users of __init_{begin,end} I think it's safe. Here's what I ended up with
on fixes.
Thanks!
commit 84814460eef9af0fb56a4698341c9cb7996a6312 (HEAD -> fixes, riscv/fixes)
gpg: Signature made Tue 06 Oct 2020 09:11:35 PM PDT
gpg: using RSA key 2B3C3747446843B24A943A7A2E1319F35FBB1889
gpg: issuer "palmer@...belt.com"
gpg: Good signature from "Palmer Dabbelt <palmer@...belt.com>" [ultimate]
gpg: aka "Palmer Dabbelt <palmerdabbelt@...gle.com>" [ultimate]
Author: Guo Ren <guoren@...ux.alibaba.com>
Date: Tue Oct 6 16:49:33 2020 +0000
riscv: Fixup bootup failure with HARDENED_USERCOPY
6184358da000 ("riscv: Fixup static_obj() fail") attempted to elide a lockdep
failure by rearranging our kernel image to place all initdata within [_stext,
_end], thus triggering lockdep to treat these as static objects. These objects
are released and eventually reallocated, causing check_kernel_text_object() to
trigger a BUG().
This backs out the change to make [_stext, _end] all-encompassing, instead just
moving initdata. This results in initdata being outside of [__init_begin,
__init_end], which means initdata can't be freed.
Link: https://lore.kernel.org/linux-riscv/1593266228-61125-1-git-send-email-guoren@kernel.org/T/#t
Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Reported-by: Aurelien Jarno <aurelien@...el32.net>
Tested-by: Aurelien Jarno <aurelien@...el32.net>
[Palmer: Clean up commit text]
Signed-off-by: Palmer Dabbelt <palmerdabbelt@...gle.com>
> static_obj() fail). When we expand static_obj include INIT_DATA,
> we also include INIT_TEXT into usercopy check kernel text:
>
> /* Is this address range in the kernel text area? */
> static inline void check_kernel_text_object(const unsigned long ptr,
> unsigned long n, bool to_user)
> {
> unsigned long textlow = (unsigned long)_stext;
> unsigned long texthigh = (unsigned long)_etext;
> unsigned long textlow_linear, texthigh_linear;
>
> if (overlaps(ptr, n, textlow, texthigh))
> usercopy_abort("kernel text", NULL, to_user, ptr - textlow, n);
>
> When INIT_TEXT/DATA are freed, new allocation will reuse these
> memory and overlaps check will be triggered.
>
> The patch met static_obj and check_kernel_text_object requirements.
>
> Link: https://lore.kernel.org/linux-riscv/1593266228-61125-1-git-send-email-guoren@kernel.org/T/#t
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Reported-by: Aurelien Jarno <aurelien@...el32.net>
> Tested-by: Aurelien Jarno <aurelien@...el32.net>
> Cc: Palmer Dabbelt <palmerdabbelt@...gle.com>
> Cc: Atish Patra <atishp@...shpatra.org>
> Cc: Andreas Schwab <schwab@...ux-m68k.org>
> ---
> arch/riscv/kernel/vmlinux.lds.S | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> index f3586e3..34d00d9 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -22,13 +22,11 @@ SECTIONS
> /* Beginning of code and text segment */
> . = LOAD_OFFSET;
> _start = .;
> - _stext = .;
> HEAD_TEXT_SECTION
> . = ALIGN(PAGE_SIZE);
>
> __init_begin = .;
> INIT_TEXT_SECTION(PAGE_SIZE)
> - INIT_DATA_SECTION(16)
> . = ALIGN(8);
> __soc_early_init_table : {
> __soc_early_init_table_start = .;
> @@ -55,6 +53,7 @@ SECTIONS
> . = ALIGN(SECTION_ALIGN);
> .text : {
> _text = .;
> + _stext = .;
> TEXT_TEXT
> SCHED_TEXT
> CPUIDLE_TEXT
> @@ -67,6 +66,8 @@ SECTIONS
> _etext = .;
> }
>
> + INIT_DATA_SECTION(16)
> +
> /* Start of data section */
> _sdata = .;
> RO_DATA(SECTION_ALIGN)
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