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Date:   Fri, 12 Apr 2019 13:17:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kernel test robot <lkp@...el.com>
Cc:     LKP <lkp@...org>, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Nadav Amit <namit@...are.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: 1808d65b55 ("asm-generic/tlb: Remove arch_tlb*_mmu()"):  BUG:
 KASAN: stack-out-of-bounds in __change_page_attr_set_clr

On Fri, Apr 12, 2019 at 12:56:33PM +0200, Peter Zijlstra wrote:
> On Thu, Apr 11, 2019 at 11:13:48PM +0200, Peter Zijlstra wrote:
> > On Thu, Apr 11, 2019 at 09:54:24PM +0200, Peter Zijlstra wrote:
> > > On Thu, Apr 11, 2019 at 09:39:06PM +0200, Peter Zijlstra wrote:
> > > > I think this bisect is bad. If you look at your own logs this patch
> > > > merely changes the failure, but doesn't make it go away.
> > > > 
> > > > Before this patch (in fact, before tip/core/mm entirely) the errror
> > > > reads like the below, which suggests there is memory corruption
> > > > somewhere, and the fingered patch just makes it trigger differently.
> > > > 
> > > > It would be very good to find the source of this corruption, but I'm
> > > > fairly certain it is not here.
> > > 
> > > I went back to v4.20 to try and find a time when the below error did not
> > > occur, but even that reliably triggers the warning.
> > 
> > So I also tested v4.19 and found that that was good, which made me
> > bisect v4.19..v4.20
> > 
> > # bad: [8fe28cb58bcb235034b64cbbb7550a8a43fd88be] Linux 4.20
> > # good: [84df9525b0c27f3ebc2ebb1864fa62a97fdedb7d] Linux 4.19
> > git bisect start 'v4.20' 'v4.19'
> > # bad: [ec9c166434595382be3babf266febf876327774d] Merge tag 'mips_fixes_4.20_1' of git://git.kernel.org/pub/scm/linux/kernel/git/mips/linux
> > git bisect bad ec9c166434595382be3babf266febf876327774d
> > # bad: [50b825d7e87f4cff7070df6eb26390152bb29537] Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
> > git bisect bad 50b825d7e87f4cff7070df6eb26390152bb29537
> > # good: [99e9acd85ccbdc8f5785f9e961d4956e96bd6aa5] Merge tag 'mlx5-updates-2018-10-17' of git://git.kernel.org/pub/scm/linux/kernel/git/saeed/linux
> > git bisect good 99e9acd85ccbdc8f5785f9e961d4956e96bd6aa5
> > # good: [c403993a41d50db1e7d9bc2d43c3c8498162312f] Merge tag 'for-linus-4.20' of https://github.com/cminyard/linux-ipmi
> > git bisect good c403993a41d50db1e7d9bc2d43c3c8498162312f
> > # good: [c05f3642f4304dd081876e77a68555b6aba4483f] Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> > git bisect good c05f3642f4304dd081876e77a68555b6aba4483f
> > # bad: [44786880df196a4200c178945c4d41675faf9fb7] Merge branch 'parisc-4.20-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux
> > git bisect bad 44786880df196a4200c178945c4d41675faf9fb7
> > # bad: [99792e0cea1ed733cdc8d0758677981e0cbebfed] Merge branch 'x86-mm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> > git bisect bad 99792e0cea1ed733cdc8d0758677981e0cbebfed
> > # good: [fec98069fb72fb656304a3e52265e0c2fc9adf87] Merge branch 'x86-cpu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> > git bisect good fec98069fb72fb656304a3e52265e0c2fc9adf87
> > # bad: [a31acd3ee8f7dbc0370bdf4a4bfef7a8c13c7542] x86/mm: Page size aware flush_tlb_mm_range()
> > git bisect bad a31acd3ee8f7dbc0370bdf4a4bfef7a8c13c7542
> > # good: [a7295fd53c39ce781a9792c9dd2c8747bf274160] x86/mm/cpa: Use flush_tlb_kernel_range()
> > git bisect good a7295fd53c39ce781a9792c9dd2c8747bf274160
> > # good: [9cf38d5559e813cccdba8b44c82cc46ba48d0896] kexec: Allocate decrypted control pages for kdump if SME is enabled
> > git bisect good 9cf38d5559e813cccdba8b44c82cc46ba48d0896
> > # good: [5b12904065798fee8b153a506ac7b72d5ebbe26c] x86/mm/doc: Clean up the x86-64 virtual memory layout descriptions
> > git bisect good 5b12904065798fee8b153a506ac7b72d5ebbe26c
> > # good: [cf089611f4c446285046fcd426d90c18f37d2905] proc/vmcore: Fix i386 build error of missing copy_oldmem_page_encrypted()
> > git bisect good cf089611f4c446285046fcd426d90c18f37d2905
> > # good: [a5b966ae42a70b194b03eaa5eaea70d8b3790c40] Merge branch 'tlb/asm-generic' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux into x86/mm
> > git bisect good a5b966ae42a70b194b03eaa5eaea70d8b3790c40
> > # first bad commit: [a31acd3ee8f7dbc0370bdf4a4bfef7a8c13c7542] x86/mm: Page size aware flush_tlb_mm_range()
> > 
> > And 'funnily' the bad patch is one of mine too :/
> > 
> > I'll go have a look at that tomorrow, because currrently I'm way past
> > tired.
> 
> OK, so the below patchlet makes it all good. It turns out that the
> provided config has:
> 
> CONFIG_X86_L1_CACHE_SHIFT=7
> 
> which then, for some obscure raisin, results in flush_tlb_mm_range()
> compiling to use 320 bytes of stack:
> 
>   sub    $0x140,%rsp
> 
> Where a 'defconfig' build results in:
> 
>   sub    $0x58,%rsp
> 
> The thing that pushes it over the edge in the above fingered patch is
> the addition of a field to struct flush_tlb_info, which grows if from 32
> to 36 bytes.
> 
> So my proposal is to basically revert that, unless we can come up with
> something that GCC can't screw up.

To clarify, 'that' is Nadav's patch:

  515ab7c41306 ("x86/mm: Align TLB invalidation info")

which turns out to be the real problem.

> ---
>  arch/x86/mm/tlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index bc4bc7b2f075..487b8474c01c 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -728,7 +728,7 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
>  {
>  	int cpu;
>  
> -	struct flush_tlb_info info __aligned(SMP_CACHE_BYTES) = {
> +	struct flush_tlb_info info = {
>  		.mm = mm,
>  		.stride_shift = stride_shift,
>  		.freed_tables = freed_tables,
> 
> 
> > > > [   10.273617] rodata_test: all tests were successful
> > > > [   10.275015] x86/mm: Checking user space page tables
> > > > [   10.295444] x86/mm: Checked W+X mappings: passed, no W+X pages found.
> > > > [   10.296334] Run /init as init process
> > > > [   10.301465] ==================================================================
> > > > [   10.302460] BUG: KASAN: stack-out-of-bounds in __unwind_start+0x7e/0x4fe
> > > > [   10.303355] Write of size 88 at addr ffff8880191efa28 by task init/1
> > > > [   10.304241]
> > > > [   10.304455] CPU: 0 PID: 1 Comm: init Not tainted 5.1.0-rc4-00288-ga131d61b43e0-dirty #10
> > > > [   10.305542] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> > > > [   10.306641] Call Trace:
> > > > [   10.306990]  print_address_description+0x9d/0x26b
> > > > [   10.307654]  ? __unwind_start+0x7e/0x4fe
> > > > [   10.308222]  ? __unwind_start+0x7e/0x4fe
> > > > [   10.308755]  __kasan_report+0x145/0x18a
> > > > [   10.309266]  ? __unwind_start+0x7e/0x4fe
> > > > [   10.309823]  kasan_report+0xe/0x12
> > > > [   10.310273]  memset+0x1f/0x31
> > > > [   10.310703]  __unwind_start+0x7e/0x4fe
> > > > [   10.311223]  ? unwind_next_frame+0x10a9/0x10a9
> > > > [   10.311839]  ? native_flush_tlb_one_user+0x54/0x95
> > > > [   10.312504]  ? kasan_unpoison_shadow+0xf/0x2e
> > > > [   10.313090]  __save_stack_trace+0x65/0xe7
> > > > [   10.313667]  ? trace_irq_enable_rcuidle+0x21/0xf5
> > > > [   10.314284]  ? tracer_hardirqs_on+0xb/0x1b
> > > > [   10.314830]  ? trace_hardirqs_on+0x2c/0x37
> > > > [   10.315369]  save_stack+0x32/0xa3
> > > > [   10.315842]  ? __put_compound_page+0x91/0x91
> > > > [   10.316458]  ? preempt_latency_start+0x22/0x68
> > > > [   10.317052]  ? free_swap_cache+0x51/0xd5
> > > > [   10.317586]  ? tlb_flush_mmu_free+0x31/0xca
> > > > [   10.318140]  ? arch_tlb_finish_mmu+0x8c/0x112
> > > > [   10.318759]  ? tlb_finish_mmu+0xc7/0xd6
> > > > [   10.319298]  ? unmap_region+0x275/0x2b9
> > > > [   10.319835]  ? special_mapping_fault+0x26d/0x26d
> > > > [   10.320448]  ? trace_irq_disable_rcuidle+0x21/0xf5
> > > > [   10.321085]  __kasan_slab_free+0xd3/0xf4
> > > > [   10.321623]  ? remove_vma+0xdf/0xe7
> > > > [   10.322105]  kmem_cache_free+0x4e/0xca
> > > > [   10.322600]  remove_vma+0xdf/0xe7
> > > > [   10.323038]  __do_munmap+0x72c/0x75e
> > > > [   10.323514]  __vm_munmap+0xd0/0x135
> > > > [   10.323980]  ? __x64_sys_brk+0x40e/0x40e
> > > > [   10.324496]  ? trace_irq_disable_rcuidle+0x21/0xf5
> > > > [   10.325160]  __x64_sys_munmap+0x6a/0x6f
> > > > [   10.325670]  do_syscall_64+0x3f0/0x462
> > > > [   10.326162]  ? syscall_return_slowpath+0x154/0x154
> > > > [   10.326810]  ? entry_SYSCALL_64_after_hwframe+0x3e/0xbe
> > > > [   10.327485]  ? trace_irq_disable_rcuidle+0x21/0xf5
> > > > [   10.328153]  ? entry_SYSCALL_64_after_hwframe+0x3e/0xbe
> > > > [   10.328873]  ? trace_hardirqs_off_caller+0x3e/0x40
> > > > [   10.329505]  ? trace_hardirqs_off_thunk+0x1a/0x1c
> > > > [   10.330162]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > > > [   10.330830] RIP: 0033:0x7efc4d707457
> > > > [   10.331306] Code: f0 ff ff 73 01 c3 48 8d 0d 5a be 20 00 31 d2 48 29 c2 89 11 48 83 c8 ff eb eb 90 90 90 90 90 90 90 90 90 b8 0b 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8d 0d 2d be 20 00 31 d2 48 29 c2 89
> > > > [   10.333711] RSP: 002b:00007fff973da398 EFLAGS: 00000203 ORIG_RAX: 000000000000000b
> > > > [   10.334728] RAX: ffffffffffffffda RBX: 00007efc4d9132c8 RCX: 00007efc4d707457
> > > > [   10.335670] RDX: 0000000000000000 RSI: 0000000000001d67 RDI: 00007efc4d90d000
> > > > [   10.336596] RBP: 00007fff973da4f0 R08: 0000000000000007 R09: 00000000ffffffff
> > > > [   10.337512] R10: 0000000000000000 R11: 0000000000000203 R12: 000000073dd74283
> > > > [   10.338457] R13: 000000073db1ab4f R14: 00007efc4d909700 R15: 00007efc4d9132c8
> > > > [   10.339373]
> > > > [   10.339585] The buggy address belongs to the page:
> > > > [   10.340224] page:ffff88801de82c48 count:0 mapcount:0 mapping:0000000000000000 index:0x0
> > > > [   10.341338] flags: 0x680000000000()
> > > > [   10.341832] raw: 0000680000000000 ffff88801de82c50 ffff88801de82c50 0000000000000000
> > > > [   10.342846] raw: 0000000000000000 0000000000000000 00000000ffffffff
> > > > [   10.343679] page dumped because: kasan: bad access detected
> > > > [   10.344415]
> > > > [   10.344629] Memory state around the buggy address:
> > > > [   10.345254]  ffff8880191ef900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > > > [   10.346245]  ffff8880191ef980: 00 00 f1 f1 f1 f1 00 f2 f2 f2 00 00 00 00 00 00
> > > > [   10.347217] >ffff8880191efa00: 00 00 00 00 00 f2 f2 f2 00 00 00 00 00 00 00 00
> > > > [   10.348152]                                   ^
> > > > [   10.348755]  ffff8880191efa80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > > > [   10.349698]  ffff8880191efb00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > > > [   10.350650] ==================================================================

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