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Date: Wed, 18 Oct 2023 23:35:27 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
linux-tip-commits@...r.kernel.org,
David Kaplan <david.kaplan@....com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
David Howells <dhowells@...hat.com>
Subject: Re: [tip: x86/bugs] x86/retpoline: Ensure default return thunk isn't
used at runtime
On Wed, Oct 18, 2023 at 10:37:47PM +0200, Borislav Petkov wrote:
> +++ b/arch/x86/kernel/alternative.c
> @@ -748,14 +748,20 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end)
> continue;
>
> op = insn.opcode.bytes[0];
> - if (op == JMP32_INSN_OPCODE)
> + if (op == JMP32_INSN_OPCODE || op == JMP8_INSN_OPCODE)
> dest = addr + insn.length + insn.immediate.value;
I can recreate (with my GCC 12) by disabling CONFIG_CALL_DEPTH_TRACKING
and CONFIG_CPU_SRSO, which puts __x86_return_thunk() close enough to the
retpolines to enable the two-byte JMP in the last retpoline. And then
booting with spectre_v2=retpoline.
(Then to force two-byte JMPs for more retpolines, I cheated and just
moved __x86_return_thunk() to right after the retpolines.)
Your WARN patch didn't seem to fix the no-output hang for me, maybe due
to recursive warnings?
I was able to get more output by changing the WARN to (ahem) WARN_ONCE,
but it's still getting into some kind of stack corruption. Full output
below. I haven't had a chance to look further, but it's worrisome that
even the WARN_ONCE isn't being recovered from.
Regardless of if we revert e92626af3234 ("x86/retpoline: Remove
.text..__x86.return_thunk section"), or do the above patch, we still
need to figure out why even WARN_ONCE() would be borking things.
Off to bed...
[ 0.403286] ------------[ cut here ]------------
[ 0.403286] missing return thunk: __x86_indirect_thunk_r12+0xa/0x20-0x0: eb 74 66 66 2e
[ 0.403286] WARNING: CPU: 0 PID: 0 at arch/x86/kernel/alternative.c:742 apply_returns+0xca/0x23a
[ 0.403286] Modules linked in:
[ 0.403286] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.6.0-rc2+ #193
[ 0.403286] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc37 04/01/2014
[ 0.403286] RIP: 0010:apply_returns+0xca/0x23a
[ 0.403286] Code: 80 3d fa e2 65 01 00 75 b4 49 89 d8 b9 05 00 00 00 48 89 ea 48 89 de 48 c7 c7 c0 35 1a 82 c6 05 dc e2 65 01 01 e8 00 2c 0a 00 <0f> 0b eb 8f f6 05 50 18 e3 01 02 74 26 0f b6 54 24 52 48 63 44 24
[ 0.403286] RSP: 0000:ffffffff82403e30 EFLAGS: 00010282
[ 0.403286] RAX: 0000000000000000 RBX: ffffffff81aa100a RCX: 0000000000000003
[ 0.403286] RDX: 0000000000000003 RSI: 0000000000000003 RDI: 0000000000000001
[ 0.403286] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
[ 0.403286] R10: 0000000000000003 R11: ffffffff82403961 R12: ffffffff82e421f4
[ 0.403286] R13: ffffffff82e42218 R14: ffffffff82411f40 R15: 0000000000093cb0
[ 0.403286] FS: 0000000000000000(0000) GS:ffff88817b600000(0000) knlGS:0000000000000000
[ 0.403286] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.403286] CR2: ffff88817ffff000 CR3: 000000000243c001 CR4: 0000000000770ef0
[ 0.403286] PKRU: 55555554
[ 0.403286] Call Trace:
[ 0.403286] <TASK>
[ 0.403286] ? __warn+0xab/0x148
[ 0.403286] ? report_bug+0x109/0x17e
[ 0.403286] ? apply_returns+0xca/0x23a
[ 0.403286] ? handle_bug+0x41/0x6f
[ 0.403286] ? exc_invalid_op+0x13/0x60
[ 0.403286] ? asm_exc_invalid_op+0x16/0x20
[ 0.403286] ? __x86_indirect_thunk_r12+0xa/0x20
[ 0.403286] ? apply_returns+0xca/0x23a
[ 0.403286] ? __x86_indirect_thunk_r12+0xa/0x20
[ 0.403286] ? __x86_indirect_thunk_r12+0x19/0x20
[ 0.403286] ? __x86_indirect_thunk_r12+0xc/0x20
[ 0.403286] alternative_instructions+0x48/0xf5
[ 0.403286] arch_cpu_finalize_init+0xca/0xeb
[ 0.403286] start_kernel+0x588/0x610
[ 0.403286] x86_64_start_reservations+0x25/0x25
[ 0.403286] x86_64_start_kernel+0x73/0x73
[ 0.403286] secondary_startup_64_no_verify+0x166/0x16b
[ 0.403286] </TASK>
[ 0.403286] irq event stamp: 116873
[ 0.403286] hardirqs last enabled at (116883): [<ffffffff811497c4>] console_unlock+0xb0/0xfe
[ 0.403286] hardirqs last disabled at (116892): [<ffffffff811497a9>] console_unlock+0x95/0xfe
[ 0.403286] softirqs last enabled at (0): [<0000000000000000>] 0x0
[ 0.403286] softirqs last disabled at (0): [<0000000000000000>] 0x0
[ 0.403286] ---[ end trace 0000000000000000 ]---
[ 0.403286] ------------[ cut here ]------------
[ 0.403286] Unconverted return thunk
[ 0.403286] WARNING: CPU: 0 PID: 0 at arch/x86/kernel/cpu/bugs.c:2855 check_thunks+0x21/0x28
[ 0.403286] Modules linked in:
[ 0.403286] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W 6.6.0-rc2+ #193
[ 0.403286] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc37 04/01/2014
[ 0.403286] RIP: 0010:check_thunks+0x21/0x28
[ 0.403286] Code: be 02 00 00 e9 3b f3 ff ff 0f 1f 44 00 00 80 3d c9 0f 65 01 00 75 15 48 c7 c7 9b 61 1a 82 c6 05 b9 0f 65 01 01 e8 c3 58 09 00 <0f> 0b c3 cc cc cc cc 89 ff e8 54 09 02 00 90 c3 cc cc cc cc 53 89
[ 0.403286] RSP: 0000:ffffffff824039f8 EFLAGS: 00010082
[ 0.403286] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000003
[ 0.403286] RDX: 0000000000000004 RSI: 0000000000000003 RDI: 0000000000000001
[ 0.403286] RBP: ffffffff82403aa8 R08: 0000000000000000 R09: 0000000000000000
[ 0.403286] R10: 7574657220646574 R11: 7265766e6f636e55 R12: ffffffff824128c0
[ 0.403286] R13: ffffffff8117bdf0 R14: ffffffff82403ab8 R15: ffffffff83097580
[ 0.403286] FS: 0000000000000000(0000) GS:ffff88817b600000(0000) knlGS:0000000000000000
[ 0.403286] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.403286] CR2: ffff88817ffff000 CR3: 000000000243c001 CR4: 0000000000770ef0
[ 0.403286] PKRU: 55555554
[ 0.403286] Call Trace:
[ 0.403286] <TASK>
[ 0.403286] ? __warn+0xab/0x148
[ 0.403286] ? report_bug+0x109/0x17e
[ 0.403286] ? check_thunks+0x21/0x28
[ 0.403286] ? handle_bug+0x41/0x6f
[ 0.403286] ? exc_invalid_op+0x13/0x60
[ 0.403286] ? asm_exc_invalid_op+0x16/0x20
[ 0.403286] ? write_profile+0x163/0x163
[ 0.403286] ? check_thunks+0x21/0x28
[ 0.403286] ? check_thunks+0x21/0x28
[ 0.403286] __x86_return_thunk+0x5/0x7f
[ 0.403286] write_profile+0x163/0x163
[ 0.403286] arch_stack_walk+0xa3/0xda
[ 0.403286] ? stack_trace_save+0x48/0x6a
[ 0.403286] stack_trace_save+0x48/0x6a
[ 0.403286] save_trace+0x60/0x27a
[ 0.403286] mark_lock+0x108/0x357
[ 0.403286] ? desc_read+0x21/0xc5
[ 0.403286] ? insn_get_prefixes+0x17f/0x248
[ 0.403286] ? insn_get_opcode+0xd8/0x13a
[ 0.403286] __lock_acquire+0x538/0x1108
[ 0.403286] ? skip_nops+0x40/0x8e
[ 0.403286] ? _vm_unmap_aliases+0x58/0x203
[ 0.403286] lock_acquire+0x12b/0x277
[ 0.403286] ? _vm_unmap_aliases+0x58/0x203
[ 0.403286] ? insn_get_displacement+0x29/0x10a
[ 0.403286] ? __copy_user_flushcache+0x1d/0x94
[ 0.403286] ? _vm_unmap_aliases+0x58/0x203
[ 0.403286] __mutex_lock+0xbb/0x3ff
[ 0.403286] ? _vm_unmap_aliases+0x58/0x203
[ 0.403286] ? tracer_hardirqs_on+0x2c/0xd8
[ 0.403286] ? text_poke_early+0x85/0x95
[ 0.403286] ? _vm_unmap_aliases+0x58/0x203
[ 0.403286] _vm_unmap_aliases+0x58/0x203
[ 0.403286] ? __copy_user_flushcache+0x1d/0x94
[ 0.403286] change_page_attr_set_clr+0xc0/0x24f
[ 0.403286] change_page_attr_set.constprop.0+0xf/0x15
[ 0.403286] set_memory_nx+0x27/0x2d
[ 0.403286] free_init_pages+0x54/0x83
[ 0.403286] alternative_instructions+0xe1/0xf5
[ 0.403286] arch_cpu_finalize_init+0xca/0xeb
[ 0.403286] start_kernel+0x588/0x610
[ 0.403286] x86_64_start_reservations+0x25/0x25
[ 0.403286] x86_64_start_kernel+0x73/0x73
[ 0.403286] secondary_startup_64_no_verify+0x166/0x16b
[ 0.403286] </TASK>
[ 0.403286] irq event stamp: 122505
[ 0.403286] hardirqs last enabled at (122505): [<ffffffff81033999>] text_poke_early+0x85/0x95
[ 0.403286] hardirqs last disabled at (122504): [<ffffffff81033986>] text_poke_early+0x72/0x95
[ 0.403286] softirqs last enabled at (0): [<0000000000000000>] 0x0
[ 0.403286] softirqs last disabled at (0): [<0000000000000000>] 0x0
[ 0.403286] ---[ end trace 0000000000000000 ]---
[ 0.403286] BUG: kernel NULL pointer dereference, address: 0000000000000011
[ 0.403286] #PF: supervisor read access in kernel mode
[ 0.403286] #PF: error_code(0x0000) - not-present page
[ 0.403286] PGD 0 P4D 0
[ 0.403286] Oops: 0000 [#1] PREEMPT SMP NOPTI
[ 0.403286] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W 6.6.0-rc2+ #193
[ 0.403286] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc37 04/01/2014
[ 0.403286] RIP: 0010:stack_trace_consume_entry+0x5/0x3c
[ 0.403286] Code: 48 89 d8 48 8b 54 24 08 65 48 2b 14 25 28 00 00 00 74 05 e8 f9 47 91 00 48 83 c4 10 5b 5d 41 5c c3 cc cc cc cc 0f 1f 44 00 00 <8b> 47 10 31 d2 3b 47 08 73 26 8b 57 0c 85 d2 74 09 ff ca 89 57 0c
[ 0.403286] RSP: 0000:ffffffff82403a08 EFLAGS: 00010082
[ 0.403286] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000003
[ 0.403286] RDX: 0000000000000004 RSI: 0000000000000003 RDI: 0000000000000001
[ 0.403286] RBP: ffffffff82403aa8 R08: 0000000000000000 R09: 0000000000000000
[ 0.403286] R10: 7574657220646574 R11: 7265766e6f636e55 R12: ffffffff824128c0
[ 0.403286] R13: ffffffff8117bdf0 R14: ffffffff82403ab8 R15: ffffffff83097580
[ 0.403286] FS: 0000000000000000(0000) GS:ffff88817b600000(0000) knlGS:0000000000000000
[ 0.403286] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.403286] CR2: 0000000000000011 CR3: 000000000243c001 CR4: 0000000000770ef0
[ 0.403286] PKRU: 55555554
[ 0.403286] Call Trace:
[ 0.403286] <TASK>
[ 0.403286] ? __die_body+0x1a/0x5c
[ 0.403286] ? page_fault_oops+0x333/0x380
[ 0.403286] ? do_user_addr_fault+0x125/0x503
[ 0.403286] ? exc_page_fault+0x168/0x19e
[ 0.403286] ? asm_exc_page_fault+0x22/0x30
[ 0.403286] ? write_profile+0x163/0x163
[ 0.403286] ? stack_trace_consume_entry+0x5/0x3c
[ 0.403286] ? write_profile+0x163/0x163
[ 0.403286] arch_stack_walk+0xa3/0xda
[ 0.403286] ? stack_trace_save+0x48/0x6a
[ 0.403286] stack_trace_save+0x48/0x6a
[ 0.403286] save_trace+0x60/0x27a
[ 0.403286] mark_lock+0x108/0x357
[ 0.403286] ? desc_read+0x21/0xc5
[ 0.403286] ? insn_get_prefixes+0x17f/0x248
[ 0.403286] ? insn_get_opcode+0xd8/0x13a
[ 0.403286] __lock_acquire+0x538/0x1108
[ 0.403286] ? skip_nops+0x40/0x8e
[ 0.403286] ? _vm_unmap_aliases+0x58/0x203
[ 0.403286] lock_acquire+0x12b/0x277
[ 0.403286] ? _vm_unmap_aliases+0x58/0x203
[ 0.403286] ? insn_get_displacement+0x29/0x10a
[ 0.403286] ? __copy_user_flushcache+0x1d/0x94
[ 0.403286] ? _vm_unmap_aliases+0x58/0x203
[ 0.403286] __mutex_lock+0xbb/0x3ff
[ 0.403286] ? _vm_unmap_aliases+0x58/0x203
[ 0.403286] ? tracer_hardirqs_on+0x2c/0xd8
[ 0.403286] ? text_poke_early+0x85/0x95
[ 0.403286] ? _vm_unmap_aliases+0x58/0x203
[ 0.403286] _vm_unmap_aliases+0x58/0x203
[ 0.403286] ? __copy_user_flushcache+0x1d/0x94
[ 0.403286] change_page_attr_set_clr+0xc0/0x24f
[ 0.403286] change_page_attr_set.constprop.0+0xf/0x15
[ 0.403286] set_memory_nx+0x27/0x2d
[ 0.403286] free_init_pages+0x54/0x83
[ 0.403286] alternative_instructions+0xe1/0xf5
[ 0.403286] arch_cpu_finalize_init+0xca/0xeb
[ 0.403286] start_kernel+0x588/0x610
[ 0.403286] x86_64_start_reservations+0x25/0x25
[ 0.403286] x86_64_start_kernel+0x73/0x73
[ 0.403286] secondary_startup_64_no_verify+0x166/0x16b
[ 0.403286] </TASK>
[ 0.403286] Modules linked in:
[ 0.403286] CR2: 0000000000000011
[ 0.403286] ---[ end trace 0000000000000000 ]---
[ 0.403286] RIP: 0010:stack_trace_consume_entry+0x5/0x3c
[ 0.403286] Code: 48 89 d8 48 8b 54 24 08 65 48 2b 14 25 28 00 00 00 74 05 e8 f9 47 91 00 48 83 c4 10 5b 5d 41 5c c3 cc cc cc cc 0f 1f 44 00 00 <8b> 47 10 31 d2 3b 47 08 73 26 8b 57 0c 85 d2 74 09 ff ca 89 57 0c
[ 0.403286] RSP: 0000:ffffffff82403a08 EFLAGS: 00010082
[ 0.403286] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000003
[ 0.403286] RDX: 0000000000000004 RSI: 0000000000000003 RDI: 0000000000000001
[ 0.403286] RBP: ffffffff82403aa8 R08: 0000000000000000 R09: 0000000000000000
[ 0.403286] R10: 7574657220646574 R11: 7265766e6f636e55 R12: ffffffff824128c0
[ 0.403286] R13: ffffffff8117bdf0 R14: ffffffff82403ab8 R15: ffffffff83097580
[ 0.403286] FS: 0000000000000000(0000) GS:ffff88817b600000(0000) knlGS:0000000000000000
[ 0.403286] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.403286] CR2: 0000000000000011 CR3: 000000000243c001 CR4: 0000000000770ef0
[ 0.403286] PKRU: 55555554
[ 0.403286] Kernel panic - not syncing: Attempted to kill the idle task!
[ 0.403286] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
--
Josh
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