Re: [PATCH 3/6] x86/entry: Use PUSH_AND_CLEAR_REGS for compat

[Guenter Roeck <linux@roeck-us.net>]

On Fri, May 06, 2022 at 02:14:34PM +0200, Peter Zijlstra wrote:
> Since the upper regs don't exist for ia32 code, preserving them
> doesn't hurt and it simplifies the code.
> 
> This doesn't add any attack surface that would not already be
> available through INT80.
> 
> Notably:
> 
>  - 32bit SYSENTER: didn't clear si, dx, cx.
> 
>  - 32bit SYSCALL, INT80: *do* clear si since the C functions don't
>    take a second argument.
> 
>  - 64bit: didn't clear si since the C functions take a second
>    argument; except the error_entry path might have only one argument,
>    so clearing si was missing here.
> 
> 32b SYSENTER should be clearing all those 3 registers, nothing uses them
> and selftests pass.
> 
> Unconditionally clear rsi since it simplifies code.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Reviewed-by: Borislav Petkov <bp@suse.de>

linux-next (next-20220519) crashes due to this patch when booting
q35:EPYC-Rome in qemu.

[   20.716975] Run /sbin/init as init process
[   20.790596] init[1]: segfault at f7fd5ca0 ip 00000000f7f5bbc7 sp 00000000ffa06aa0 error 7 in libc.so[f7f51000+4e000]
[   20.793487] Code: 8a 44 24 10 88 41 ff 8b 44 24 10 83 c4 2c 5b 5e 5f 5d c3 53 83 ec 08 8b 5c 24 10 81 fb 00 f0 ff ff 76 0c e8 ba dc ff ff f7 db <89> 18 83 cb ff 83 c4 08 89 d8 5b c3 e8 81 60 ff ff 05 28 84 07 00
[   20.796332] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
[   20.796621] CPU: 1 PID: 1 Comm: init Tainted: G        W         5.18.0-rc7-next-20220519 #1
[   20.796724] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
[   20.796724] Call Trace:
[   20.796724]  <TASK>
[   20.796724]  dump_stack_lvl+0x57/0x7d
[   20.796724]  panic+0x10f/0x28d
[   20.796724]  do_exit.cold+0x18/0x48
[   20.796724]  do_group_exit+0x2e/0xb0
[   20.796724]  get_signal+0xb6d/0xb80
[   20.796724]  arch_do_signal_or_restart+0x31/0x760
[   20.796724]  ? show_opcodes.cold+0x1c/0x21
[   20.796724]  ? force_sig_fault+0x49/0x70
[   20.796724]  exit_to_user_mode_prepare+0x131/0x1a0
[   20.796724]  irqentry_exit_to_user_mode+0x5/0x30
[   20.796724]  asm_exc_page_fault+0x27/0x30
[   20.796724] RIP: 0023:0xf7f5bbc7
[   20.796724] Code: 8a 44 24 10 88 41 ff 8b 44 24 10 83 c4 2c 5b 5e 5f 5d c3 53 83 ec 08 8b 5c 24 10 81 fb 00 f0 ff ff 76 0c e8 ba dc ff ff f7 db <89> 18 83 cb ff 83 c4 08 89 d8 5b c3 e8 81 60 ff ff 05 28 84 07 00
[   20.796724] RSP: 002b:00000000ffa06aa0 EFLAGS: 00000217
[   20.796724] RAX: 00000000f7fd5ca0 RBX: 000000000000000c RCX: 0000000000001000
[   20.796724] RDX: 0000000000000001 RSI: 00000000f7fd5b60 RDI: 00000000f7fd5b60
[   20.796724] RBP: 00000000f7fd1c1c R08: 0000000000000000 R09: 0000000000000000
[   20.796724] R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
[   20.796724] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   20.796724]  </TASK>
[   20.796724] Kernel Offset: 0x33000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)

Bisect log attached. Reverting the patch fixes the problem.

Guenter

---
# bad: [21498d01d045c5b95b93e0a0625ae965b4330ebe] Add linux-next specific files for 20220519
# good: [42226c989789d8da4af1de0c31070c96726d990c] Linux 5.18-rc7
git bisect start 'HEAD' 'v5.18-rc7'
# good: [00ad3ec718d0a85b8fe6b317f07e585650e05073] Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/cryptodev-2.6.git
git bisect good 00ad3ec718d0a85b8fe6b317f07e585650e05073
# bad: [7bbdec75300e073a8fa14d19409af4b43bbaff17] Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
git bisect bad 7bbdec75300e073a8fa14d19409af4b43bbaff17
# good: [c298441f72cd14bbe74ac49a5c60ecf302cc2f97] Merge branch 'drm-next' of https://gitlab.freedesktop.org/agd5f/linux
git bisect good c298441f72cd14bbe74ac49a5c60ecf302cc2f97
# good: [e261ae308e94dc89db3f473db29662942a4dd532] Merge branch 'for-next' of git://git.kernel.dk/linux-block.git
git bisect good e261ae308e94dc89db3f473db29662942a4dd532
# good: [ba821c4223c38f4ec1cc2c7151c8abd4c70e3178] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git
git bisect good ba821c4223c38f4ec1cc2c7151c8abd4c70e3178
# good: [2b0b069fc23047b66e1bf6ffd60e7ea5d4e2f484] Merge branch into tip/master: 'smp/core'
git bisect good 2b0b069fc23047b66e1bf6ffd60e7ea5d4e2f484
# bad: [7e2492890410e54a44b5cea9d34ecca45bf74890] Merge branch into tip/master: 'locking/core'
git bisect bad 7e2492890410e54a44b5cea9d34ecca45bf74890
# bad: [9e20f60bad4afb3e1f368e9a61d9813210ce6a29] Merge branch into tip/master: 'x86/cleanups'
git bisect bad 9e20f60bad4afb3e1f368e9a61d9813210ce6a29
# bad: [ab07ef45e638d9fdffbdd2f50521f73096acf2f1] Merge branch into tip/master: 'x86/asm'
git bisect bad ab07ef45e638d9fdffbdd2f50521f73096acf2f1
# good: [81893ca70cddbbce7cde243e0c70de6917b82956] Merge branch into tip/master: 'timers/core'
git bisect good 81893ca70cddbbce7cde243e0c70de6917b82956
# good: [d205222eb6a8e5e70c21200beb81c6e19ec211d6] x86/entry: Simplify entry_INT80_compat()
git bisect good d205222eb6a8e5e70c21200beb81c6e19ec211d6
# bad: [e2ef115813c34ea5380ac5b4879f515070150210] objtool: Fix STACK_FRAME_NON_STANDARD reloc type
git bisect bad e2ef115813c34ea5380ac5b4879f515070150210
# bad: [1b331eeea7b8676fc5dbdf80d0a07e41be226177] x86/entry: Remove skip_r11rcx
git bisect bad 1b331eeea7b8676fc5dbdf80d0a07e41be226177
# bad: [8c42819b61b8340cff0643e65b5ce6a4144ab155] x86/entry: Use PUSH_AND_CLEAR_REGS for compat
git bisect bad 8c42819b61b8340cff0643e65b5ce6a4144ab155
# first bad commit: [8c42819b61b8340cff0643e65b5ce6a4144ab155] x86/entry: Use PUSH_AND_CLEAR_REGS for compat