From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Yonghong Song <yhs@fb.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
stable@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 01/11] x86/fault: Fix AMD erratum #91 errata fixup for user code
Date: Mon, 1 Feb 2021 21:31:46 +0100 [thread overview]
Message-ID: <20210201203146.GC14590@zn.tnic> (raw)
In-Reply-To: <7aaa6ff8d29faea5a9324a85e5ad6c41c654e9e0.1612113550.git.luto@kernel.org>
On Sun, Jan 31, 2021 at 09:24:32AM -0800, Andy Lutomirski wrote:
> The recent rework of probe_kernel_read() and its conversion to
Judging by
25f12ae45fc1 ("maccess: rename probe_kernel_address to get_kernel_nofault")
I think you mean probe_kernel_address() above and below.
> get_kernel_nofault() inadvertently broke is_prefetch(). We were using
Let's drop the "we" pls and switch to passive voice.
> probe_kernel_read() as a sloppy "read user or kernel memory" helper, but it
> doens't do that any more. The new get_kernel_nofault() reads *kernel*
> memory only, which completely broke is_prefetch() for user access.
>
> Adjust the code to the the correct accessor based on access mode. The
s/the //
> manual address bounds check is no longer necessary, since the accessor
> helpers (get_user() / get_kernel_nofault()) do the right thing all by
> themselves. As a bonus, by using the correct accessor, we don't need the
> open-coded address bounds check.
>
> While we're at it, disable the workaround on all CPUs except AMD Family
> 0xF. By my reading of the Revision Guide for AMD Athlon™ 64 and AMD
> Opteron™ Processors, only family 0xF is affected.
Yah, actually, only !NPT K8s have the erratum listed, i.e., CPU models <
0x40, AFAICT.
I.e., your test should be:
struct cpuinfo_x86 *c = &boot_cpu_data;
...
/* Erratum #91 on AMD K8, pre-NPT CPUs */
if (likely(c->x86_vendor != X86_VENDOR_AMD ||
c->x86 != 0xf ||
c->x86_model >= 0x40))
return 0;
I can try to dig out such a machine to test this on if you wanna. We
might still have one collecting dust somewhere in a corner...
> Fixes: eab0c6089b68 ("maccess: unify the probe kernel arch hooks")
> Cc: stable@vger.kernel.org
@stable because theoretically without that fix, kernel should explode on
those machines when it #PFs on a prefetch insn in user mode?
Hmm, yap, probably...
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/mm/fault.c | 31 +++++++++++++++++++++----------
> 1 file changed, 21 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 106b22d1d189..50dfdc71761e 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -54,7 +54,7 @@ kmmio_fault(struct pt_regs *regs, unsigned long addr)
> * 32-bit mode:
> *
> * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
> - * Check that here and ignore it.
> + * Check that here and ignore it. This is AMD erratum #91.
> *
> * 64-bit mode:
> *
> @@ -83,11 +83,7 @@ check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
> #ifdef CONFIG_X86_64
> case 0x40:
> /*
> - * In AMD64 long mode 0x40..0x4F are valid REX prefixes
> - * Need to figure out under what instruction mode the
> - * instruction was issued. Could check the LDT for lm,
> - * but for now it's good enough to assume that long
> - * mode only uses well known segments or kernel.
> + * In 64-bit mode 0x40..0x4F are valid REX prefixes
> */
> return (!user_mode(regs) || user_64bit_mode(regs));
> #endif
Yah, no need to convert that to the insn decoder - that can die together
with the hardware it is supposed to query...
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2021-02-01 20:32 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-31 17:24 [PATCH 00/11] x86/fault: Cleanups and robustifications Andy Lutomirski
2021-01-31 17:24 ` [PATCH 01/11] x86/fault: Fix AMD erratum #91 errata fixup for user code Andy Lutomirski
2021-02-01 9:05 ` Christoph Hellwig
2021-02-01 20:31 ` Borislav Petkov [this message]
2021-01-31 17:24 ` [PATCH 02/11] x86/fault: Fold mm_fault_error() into do_user_addr_fault() Andy Lutomirski
2021-01-31 17:24 ` [PATCH 03/11] x86/fault/32: Move is_f00f_bug() do do_kern_addr_fault() Andy Lutomirski
2021-02-03 14:44 ` Borislav Petkov
2021-01-31 17:24 ` [PATCH 04/11] x86/fault: Document the locking in the fault_signal_pending() path Andy Lutomirski
2021-01-31 17:24 ` [PATCH 05/11] x86/fault: Correct a few user vs kernel checks wrt WRUSS Andy Lutomirski
2021-02-03 15:48 ` Borislav Petkov
2021-01-31 17:24 ` [PATCH 06/11] x86/fault: Improve kernel-executing-user-memory handling Andy Lutomirski
2021-02-01 9:08 ` Christoph Hellwig
2021-02-02 1:00 ` Andy Lutomirski
2021-02-03 16:01 ` Borislav Petkov
2021-02-03 16:23 ` Borislav Petkov
2021-01-31 17:24 ` [PATCH 07/11] x86/fault: Split the OOPS code out from no_context() Andy Lutomirski
2021-02-03 18:56 ` Borislav Petkov
2021-02-03 19:29 ` Andy Lutomirski
2021-02-03 19:46 ` Borislav Petkov
2021-02-09 20:09 ` Andy Lutomirski
2021-01-31 17:24 ` [PATCH 08/11] x86/fault: Bypass no_context() for implicit kernel faults from usermode Andy Lutomirski
2021-01-31 17:24 ` [PATCH 09/11] x86/fault: Rename no_context() to kernelmode_fixup_or_oops() Andy Lutomirski
2021-02-01 9:14 ` Christoph Hellwig
2021-02-02 1:01 ` Andy Lutomirski
2021-02-03 19:39 ` Borislav Petkov
2021-02-03 19:53 ` Andy Lutomirski
2021-02-03 20:07 ` Borislav Petkov
2021-02-03 20:14 ` Andy Lutomirski
2021-02-03 20:25 ` Borislav Petkov
2021-01-31 17:24 ` [PATCH 10/11] x86/fault: Don't run fixups for SMAP violations Andy Lutomirski
2021-02-03 19:50 ` Borislav Petkov
2021-01-31 17:24 ` [PATCH 11/11] x86/fault: Don't look for extable entries for SMEP violations Andy Lutomirski
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