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Message-ID: <202207131136.AFA428CA@keescook>
Date: Wed, 13 Jul 2022 11:44:14 -0700
From: Kees Cook <keescook@...omium.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: kernel test robot <oliver.sang@...el.com>,
Borislav Petkov <bp@...e.de>,
Josh Poimboeuf <jpoimboe@...nel.org>,
LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
lkp@...el.com
Subject: Re: [x86,static_call] ee88d363d1:
WARNING:at_arch/x86/kernel/alternative.c:#apply_returns
On Wed, Jul 13, 2022 at 02:28:55PM +0200, Peter Zijlstra wrote:
> On Wed, Jul 13, 2022 at 04:02:15PM +0800, kernel test robot wrote:
>
> > [ 22.065014][ T0] ------------[ cut here ]------------
> > [ 22.066738][ T0] WARNING: CPU: 0 PID: 0 at arch/x86/kernel/alternative.c:557 apply_returns (arch/x86/kernel/alternative.c:557 (discriminator 1))
> > [ 22.069534][ T0] Modules linked in:
> > [ 22.070738][ T0] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.19.0-rc4-00008-gee88d363d156 #1
> > [ 22.072739][ T0] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-4 04/01/2014
> > [ 22.074741][ T0] RIP: 0010:apply_returns (arch/x86/kernel/alternative.c:557 (discriminator 1))
> > [ 22.076739][ T0] Code: ff ff 74 cb 48 83 c5 04 49 39 ee 0f 87 81 fe ff ff e9 22 ff ff ff 0f 0b 48 83 c5 04 49 39 ee 0f 87 6d fe ff ff e9 0e ff ff ff <0f> 0b 48 83 c5 04 49 39 ee 0f 87 59 fe ff ff e9 fa fe ff ff 48 89
> > All code
> > ========
> > 0: ff (bad)
> > 1: ff 74 cb 48 pushq 0x48(%rbx,%rcx,8)
> > 5: 83 c5 04 add $0x4,%ebp
> > 8: 49 39 ee cmp %rbp,%r14
> > b: 0f 87 81 fe ff ff ja 0xfffffffffffffe92
> > 11: e9 22 ff ff ff jmpq 0xffffffffffffff38
> > 16: 0f 0b ud2
> > 18: 48 83 c5 04 add $0x4,%rbp
> > 1c: 49 39 ee cmp %rbp,%r14
> > 1f: 0f 87 6d fe ff ff ja 0xfffffffffffffe92
> > 25: e9 0e ff ff ff jmpq 0xffffffffffffff38
> > 2a:* 0f 0b ud2 <-- trapping instruction
> > 2c: 48 83 c5 04 add $0x4,%rbp
> > 30: 49 39 ee cmp %rbp,%r14
> > 33: 0f 87 59 fe ff ff ja 0xfffffffffffffe92
> > 39: e9 fa fe ff ff jmpq 0xffffffffffffff38
> > 3e: 48 rex.W
> > 3f: 89 .byte 0x89
> >
> > Code starting with the faulting instruction
> > ===========================================
> > 0: 0f 0b ud2
> > 2: 48 83 c5 04 add $0x4,%rbp
> > 6: 49 39 ee cmp %rbp,%r14
> > 9: 0f 87 59 fe ff ff ja 0xfffffffffffffe68
> > f: e9 fa fe ff ff jmpq 0xffffffffffffff0e
> > 14: 48 rex.W
> > 15: 89 .byte 0x89
> > [ 22.078738][ T0] RSP: 0000:ffffffffa2807dc0 EFLAGS: 00010202
> > [ 22.080737][ T0] RAX: 0000000000000000 RBX: ffffffffa1b8fe05 RCX: 0000000000000000
> > [ 22.082546][ T0] RDX: 000000000000000f RSI: ffffffffa184a3e0 RDI: ffffffffa1b8fe05
> > [ 22.083738][ T0] RBP: ffffffffa42851e8 R08: 0000000000000001 R09: ffffffffa1b8fe05
> > [ 22.086491][ T0] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffffa1b8fe00
> > [ 22.087738][ T0] R13: dffffc0000000000 R14: ffffffffa4299890 R15: 1ffffffff4500fbb
> > [ 22.089739][ T0] FS: 0000000000000000(0000) GS:ffff888396600000(0000) knlGS:0000000000000000
> > [ 22.091743][ T0] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [ 22.093738][ T0] CR2: ffff88843ffff000 CR3: 00000003a562a000 CR4: 00000000000006f0
> > [ 22.095753][ T0] Call Trace:
> > [ 22.097742][ T0] <TASK>
> > [ 22.098765][ T0] ? rwlock_bug+0xc0/0xc0
> > [ 22.100230][ T0] ? apply_retpolines (arch/x86/kernel/alternative.c:538)
> > [ 22.101791][ T0] ? int3_exception_notify (arch/x86/kernel/alternative.c:849)
> > [ 22.103261][ T0] ? check_bugs (arch/x86/kernel/cpu/bugs.c:149)
> > [ 22.104751][ T0] alternative_instructions (arch/x86/kernel/alternative.c:932)
> > [ 22.106766][ T0] check_bugs (arch/x86/kernel/cpu/bugs.c:159)
> > [ 22.108244][ T0] start_kernel (init/main.c:1132)
> > [ 22.109747][ T0] secondary_startup_64_no_verify (arch/x86/kernel/head_64.S:358)
> > [ 22.111300][ T0] </TASK>
> > [ 22.112742][ T0] irq event stamp: 87769
> > [ 22.113741][ T0] hardirqs last enabled at (87781): __up_console_sem (arch/x86/include/asm/irqflags.h:45 (discriminator 1) arch/x86/include/asm/irqflags.h:80 (discriminator 1) arch/x86/include/asm/irqflags.h:138 (discriminator 1) kernel/printk/printk.c:264 (discriminator 1))
> > [ 22.115740][ T0] hardirqs last disabled at (87794): __up_console_sem (kernel/printk/printk.c:262 (discriminator 1))
> > [ 22.117739][ T0] softirqs last enabled at (2774): cgroup_idr_alloc+0x5b/0x1c0
> > [ 22.119739][ T0] softirqs last disabled at (2772): cgroup_idr_alloc+0x2e/0x1c0
> > [ 22.121741][ T0] ---[ end trace 0000000000000000 ]---
>
>
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index d6858533e6e5..ff309e829192 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -555,8 +555,10 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end)
> dest = addr + insn.length + insn.immediate.value;
>
> if (__static_call_fixup(addr, op, dest) ||
> - WARN_ON_ONCE(dest != &__x86_return_thunk))
> + WARN_ON_ONCE(dest != &__x86_return_thunk)) {
> + printk("XXX: %pS %pS : %*ph", addr, dest, 5, addr);
> continue;
> + }
>
> DPRINTK("return thunk at: %pS (%px) len: %d to: %pS",
> addr, addr, insn.length,
>
> Gets me:
>
> [ 2.559091][ T0] ---[ end trace 0000000000000000 ]---
> [ 2.561092][ T0] XXX: lkdtm_rodata_do_nothing+0x0/0x1240 lkdtm_rodata_do_nothing+0x5/0x1240 : e9 00 00 00 00
>
> which is a result of:
>
> drivers/misc/lkdtm/Makefile:OBJCOPYFLAGS_rodata_objcopy.o := \
> drivers/misc/lkdtm/Makefile: --rename-section .noinstr.text=.rodata,alloc,readonly,load,contents
>
> which makes that:
>
> 0000000000000000 <lkdtm_rodata_do_nothing>:
> 0: e9 00 00 00 00 jmp 5 <lkdtm_rodata_do_nothing+0x5> 1: R_X86_64_PLT32 __x86_return_thunk-0x4
>
> remains unresolved.
>
> Kees, what's up with that thing, this is 'weird' at best.
Whee. Yeah, this is a regression test for validating that the .data
section is not executable. It's designed to be arch-agnostic to avoid
needing to know how to return from a function call.
Is there some way for this to opt out of the thunk and leave it a bare
"ret"?
--
Kees Cook
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