From: Arvind Sankar <nivedita@alum.mit.edu>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Borislav Petkov <bp@alien8.de>,
Peter Zijlstra <peterz@infradead.org>,
Jakub Jelinek <jakub@redhat.com>,
Sergei Trofimovich <slyfox@gentoo.org>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>,
x86@kernel.org
Subject: Re: [PATCH] x86: fix early boot crash on gcc-10
Date: Mon, 16 Mar 2020 15:53:41 -0400 [thread overview]
Message-ID: <20200316195340.GA768497@rani.riverdale.lan> (raw)
In-Reply-To: <20200316185418.GA372474@rani.riverdale.lan>
On Mon, Mar 16, 2020 at 02:54:21PM -0400, Arvind Sankar wrote:
> On Mon, Mar 16, 2020 at 02:20:00PM -0400, Arvind Sankar wrote:
> > On Mon, Mar 16, 2020 at 06:54:50PM +0100, Borislav Petkov wrote:
> > > On Mon, Mar 16, 2020 at 02:42:34PM +0100, Peter Zijlstra wrote:
> > > > Right I know, I looked for it recently :/ But since this is new in 10
> > > > and 10 isn't released yet, I figured someone can add the attribute
> > > > before it does get released.
> > >
> > > Yes, that would be a good solution.
> > >
> > > I looked at what happens briefly after building gcc10 from git and IINM,
> > > the function in question - start_secondary() - already gets the stack
> > > canary asm glue added so it checks for a stack canary.
> > >
> > > However, the stack canary value itself gets set later in that same
> > > function:
> > >
> > > /* to prevent fake stack check failure in clock setup */
> > > boot_init_stack_canary();
> > >
> > > so the asm glue which checks for it would need to reload the newly
> > > computed canary value (it is 0 before we compute it and thus the
> > > mismatch).
> > >
> > > So having a way to state "do not add stack canary checking to this
> > > particular function" would be optimal. And since you already have the
> > > "stack_protect" function attribute I figure adding a "no_stack_protect"
> > > one should be easy...
> > >
> > > > > Or of course you could add noinline attribute to whatever got inlined
> > > > > and contains some array or addressable variable that whatever
> > > > > -fstack-protector* mode kernel uses triggers it. With -fstack-protector-all
> > > > > it would never work even in the past I believe.
> > > >
> > > > I don't think the kernel supports -fstack-protector-all, but I could be
> > > > mistaken.
> > >
> > > The other thing I was thinking was to carve out only that function into
> > > a separate compilation unit and disable stack protector only for it.
> > >
> > > All IMHO of course.
> > >
> > > Thx.
> > >
> > > --
> > > Regards/Gruss,
> > > Boris.
> > >
> > > https://people.kernel.org/tglx/notes-about-netiquette
> >
> > With STACKPROTECTOR_STRONG, gcc9 (at least gentoo's version, not sure if
> > they have some patches that affect it) already adds stack canary into
> > start_secondary. Not sure why it doesn't panic already with gcc9?
> >
> > 00000000000008f0 <start_secondary>:
> > 8f0: 53 push %rbx
> > 8f1: 48 83 ec 10 sub $0x10,%rsp
> > 8f5: 65 48 8b 04 25 28 00 mov %gs:0x28,%rax
> > 8fc: 00 00
> > 8fe: 48 89 44 24 08 mov %rax,0x8(%rsp)
> > 903: 31 c0 xor %eax,%eax
> > ...
> > a2e: e8 00 00 00 00 callq a33 <start_secondary+0x143>
> > a2f: R_X86_64_PLT32 cpu_startup_entry-0x4
> > a33: 48 8b 44 24 08 mov 0x8(%rsp),%rax
> > a38: 65 48 33 04 25 28 00 xor %gs:0x28,%rax
> > a3f: 00 00
> > a41: 75 12 jne a55 <start_secondary+0x165>
> > a43: 48 83 c4 10 add $0x10,%rsp
> > a47: 5b pop %rbx
> > a48: c3 retq
> > a49: 0f 01 1d 00 00 00 00 lidt 0x0(%rip) # a50 <start_secondary+0x160>
> > a4c: R_X86_64_PC32 debug_idt_descr-0x4
> > a50: e9 cb fe ff ff jmpq 920 <start_secondary+0x30>
> > a55: e8 00 00 00 00 callq a5a <start_secondary+0x16a>
> > a56: R_X86_64_PLT32 __stack_chk_fail-0x4
>
> Wait a sec, this function calls cpu_startup_entry as the last thing it
> does, which should never return, and hence the stack canary value should
> never get checked.
>
> How does the canary get checked with the gcc10 code?
>
> boot_init_stack_canary depends on working if called from functions that
> don't return. If that doesn't work with gcc10, we need to disable stack
> protector for the other callpoints too -- start_kernel in init/main.c
> and cpu_bringup_and_idle in arch/x86/xen/smp_pv.c.
>
> /*
> * Initialize the stackprotector canary value.
> *
> * NOTE: this must only be called from functions that never return,
> * and it must always be inlined.
> */
> static __always_inline void boot_init_stack_canary(void)
Ugh, gcc10 tail-call optimizes the cpu_startup_entry call, and so checks
the canary before jumping out. The xen one will need to have stack
protector disabled too. It doesn't optimize the arch_call_rest_init call
in start_kernel for some reason, but we should probably disable it there
too.
a06: 0f ae f8 sfence
a09: 48 8b 44 24 08 mov 0x8(%rsp),%rax
a0e: 65 48 2b 04 25 28 00 sub %gs:0x28,%rax
a15: 00 00
a17: 75 1b jne a34 <start_secondary+0x164>
a19: 48 83 c4 10 add $0x10,%rsp
a1d: bf 8d 00 00 00 mov $0x8d,%edi
a22: 5b pop %rbx
a23: e9 00 00 00 00 jmpq a28 <start_secondary+0x158>
a24: R_X86_64_PLT32 cpu_startup_entry-0x4
a28: 0f 01 1d 00 00 00 00 lidt 0x0(%rip) # a2f <start_secondary+0x15f>
a2b: R_X86_64_PC32 debug_idt_descr-0x4
a2f: e9 cc fe ff ff jmpq 900 <start_secondary+0x30>
a34: e8 00 00 00 00 callq a39 <start_secondary+0x169>
a35: R_X86_64_PLT32 __stack_chk_fail-0x4
next prev parent reply other threads:[~2020-03-16 19:53 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-14 16:44 [PATCH] x86: fix early boot crash on gcc-10 Sergei Trofimovich
2020-03-16 13:04 ` Peter Zijlstra
2020-03-16 13:26 ` Jakub Jelinek
2020-03-16 13:42 ` Peter Zijlstra
2020-03-16 17:54 ` Borislav Petkov
2020-03-16 18:03 ` Jakub Jelinek
2020-03-17 14:36 ` Borislav Petkov
2020-03-17 14:39 ` Jakub Jelinek
2020-03-17 14:49 ` Borislav Petkov
2020-03-17 16:35 ` David Laight
2020-03-25 13:31 ` Borislav Petkov
2020-03-26 21:54 ` Sergei Trofimovich
2020-03-26 22:35 ` Borislav Petkov
2020-03-28 8:48 ` [PATCH v2] " Sergei Trofimovich
2020-04-13 14:15 ` [tip: x86/urgent] x86: Fix " tip-bot2 for Sergei Trofimovich
2020-04-13 16:35 ` [PATCH v2] x86: fix " Borislav Petkov
2020-04-14 13:50 ` Michael Matz
2020-04-15 7:48 ` Borislav Petkov
2020-04-15 14:53 ` Michael Matz
2020-04-15 22:19 ` Sergei Trofimovich
2020-04-17 7:57 ` Borislav Petkov
2020-04-17 8:07 ` Jakub Jelinek
2020-04-17 8:42 ` Borislav Petkov
2020-04-17 8:58 ` Jakub Jelinek
2020-04-17 9:09 ` Borislav Petkov
2020-04-17 18:15 ` Nick Desaulniers
2020-04-17 18:22 ` Nick Desaulniers
2020-04-17 19:06 ` Jakub Jelinek
2020-04-17 19:49 ` Nick Desaulniers
2020-04-17 19:53 ` Nick Desaulniers
2020-04-20 14:04 ` Michael Matz
2020-04-22 10:23 ` Borislav Petkov
2020-04-22 11:40 ` Peter Zijlstra
2020-04-22 13:49 ` Borislav Petkov
2020-04-22 13:55 ` Jakub Jelinek
2020-04-22 14:16 ` Martin Liška
2020-04-22 15:06 ` Michael Matz
2020-04-22 16:53 ` Borislav Petkov
2020-04-22 17:02 ` Jakub Jelinek
2020-04-22 18:47 ` Nick Desaulniers
2020-04-22 18:55 ` Nick Desaulniers
2020-04-22 19:21 ` Borislav Petkov
2020-04-22 21:05 ` Nick Desaulniers
2020-04-22 21:26 ` Borislav Petkov
2020-04-22 22:57 ` Nick Desaulniers
2020-04-23 12:53 ` Borislav Petkov
2020-04-23 16:12 ` [PATCH] x86: Fix early boot crash on gcc-10, next try Borislav Petkov
2020-04-23 17:30 ` Borislav Petkov
2020-04-23 18:02 ` Nick Desaulniers
2020-04-23 18:27 ` Borislav Petkov
2020-04-27 11:37 ` [tip: x86/build] x86/build: Check whether the compiler is sane tip-bot2 for Borislav Petkov
2020-04-23 19:40 ` [PATCH] x86: Fix early boot crash on gcc-10, next try Kees Cook
2020-04-25 1:46 ` Arvind Sankar
2020-04-25 8:57 ` Borislav Petkov
2020-04-25 11:09 ` Jürgen Groß
2020-04-25 15:04 ` Arvind Sankar
2020-04-25 17:31 ` Borislav Petkov
2020-04-25 17:52 ` Borislav Petkov
2020-04-27 17:07 ` David Laight
2020-04-25 18:37 ` Segher Boessenkool
2020-04-25 18:53 ` Borislav Petkov
2020-04-25 19:15 ` Segher Boessenkool
2020-04-25 22:17 ` Borislav Petkov
2020-04-25 22:25 ` Arvind Sankar
2020-04-17 10:38 ` [PATCH v2] x86: fix early boot crash on gcc-10 Peter Zijlstra
2020-04-18 13:12 ` David Laight
2020-04-17 10:41 ` Peter Zijlstra
2020-03-16 18:20 ` [PATCH] " Arvind Sankar
2020-03-16 18:54 ` Arvind Sankar
2020-03-16 19:53 ` Arvind Sankar [this message]
2020-03-16 20:08 ` Jakub Jelinek
2020-03-16 20:40 ` Arvind Sankar
2020-03-16 22:12 ` Sergei Trofimovich
2020-03-17 11:46 ` Jakub Jelinek
2020-03-17 18:10 ` Sergei Trofimovich
2020-03-16 18:22 ` Arvind Sankar
2020-03-26 23:16 ` [PATCH v2] " Sergei Trofimovich
2020-04-27 11:37 ` [tip: x86/build] x86: Fix early boot crash on gcc-10, next try tip-bot2 for Borislav Petkov
2020-05-15 11:20 ` [tip: x86/urgent] x86: Fix early boot crash on gcc-10, third try tip-bot2 for Borislav Petkov
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