| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20231016162609.wfkfsams23exesvs@box.shutemov.name>
Date: Mon, 16 Oct 2023 19:26:09 +0300
From: kirill.shutemov@...ux.intel.com
To: "Compostella, Jeremy" <jeremy.compostella@...el.com>
Cc: "Huang, Kai" <kai.huang@...el.com>,
"mingo@...nel.org" <mingo@...nel.org>,
"Li, Xin3" <xin3.li@...el.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>
Subject: Re: [PATCH v3 1/2] x86/cpu/intel: Fix MTRR verification for TME
enabled platforms
On Mon, Oct 16, 2023 at 09:14:35AM -0700, Compostella, Jeremy wrote:
> <kirill.shutemov@...ux.intel.com> writes:
>
> > On Fri, Oct 13, 2023 at 04:03:02PM -0700, Compostella, Jeremy wrote:
> >> "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com> writes:
> >> > On Tue, Oct 03, 2023 at 02:06:52AM +0000, Huang, Kai wrote:
> >> >> On Tue, 2023-10-03 at 01:47 +0300, kirill.shutemov@...ux.intel.com wrote:
> >> >> > On Fri, Sep 29, 2023 at 09:14:00AM +0000, Huang, Kai wrote:
> >> >> > > On Thu, 2023-09-28 at 15:30 -0700, Compostella, Jeremy wrote:
> >> >> > > > On TME enabled platform, BIOS publishes MTRR taking into account Total
> >> >> > > > Memory Encryption (TME) reserved bits.
> >> >> > > >
> >> >> > > > generic_get_mtrr() performs a sanity check of the MTRRs relying on the
> >> >> > > > `phys_hi_rsvd' variable which is set using the cpuinfo_x86 structure
> >> >> > > > `x86_phys_bits' field. But at the time the generic_get_mtrr()
> >> >> > > > function is ran the `x86_phys_bits' has not been updated by
> >> >> > > > detect_tme() when TME is enabled.
> >> >> > > >
> >> >> > > > Since the x86_phys_bits does not reflect yet the real maximal physical
> >> >> > > > address size yet generic_get_mtrr() complains by logging the following
> >> >> > > > messages.
> >> >> > > >
> >> >> > > > mtrr: your BIOS has configured an incorrect mask, fixing it.
> >> >> > > > mtrr: your BIOS has configured an incorrect mask, fixing it.
> >> >> > > > [...]
> >> >> > > >
> >> >> > > > In such a situation, generic_get_mtrr() returns an incorrect size but
> >> >> > > > no side effect were observed during our testing.
> >> >> > > >
> >> >> > > > For `x86_phys_bits' to be updated before generic_get_mtrr() runs,
> >> >> > > > move the detect_tme() call from init_intel() to early_init_intel().
> >> >> > >
> >> >> > > Hi,
> >> >> > >
> >> >> > > This move looks good to me, but +Kirill who is the author of detect_tme() for
> >> >> > > further comments.
> >> >> > >
> >> >> > > Also I am not sure whether it's worth to consider to move this to
> >> >> > > get_cpu_address_sizes(), which calculates the virtual/physical address sizes.
> >> >> > > Thus it seems anything that can impact physical address size
> >> >> > > could be put there.
> >> >> >
> >> >> > Actually, I am not sure how this patch works. AFAICS after the patch we
> >> >> > have the following callchain:
> >> >> >
> >> >> > early_identify_cpu()
> >> >> > this_cpu->c_early_init() (which is early_init_init())
> >> >> > detect_tme()
> >> >> > c->x86_phys_bits -= keyid_bits;
> >> >> > get_cpu_address_sizes(c);
> >> >> > c->x86_phys_bits = eax & 0xff;
> >> >> >
> >> >> > Looks like get_cpu_address_sizes() would override what detect_tme() does.
> >> >>
> >> >> After this patch, early_identify_cpu() calls get_cpu_address_sizes() first and
> >> >> then calls c_early_init(), which calls detect_tme().
> >> >>
> >> >> So looks no override. No?
> >>
> >> No override indeed as get_cpu_address_sizes() is always called before
> >> early_init_intel or init_intel().
> >>
> >> - init/main.c::start_kernel()
> >> - arch/x86/kernel/setup.c::setup_arch()
> >> - arch/x86/kernel/cpu/common.c::early_cpu_init()
> >> - early_identify_cpu()
> >> - get_cpu_address_sizes(c)
> >> c->x86_phys_bits = eax & 0xff;
> >> - arch/x86/kernel/cpu/intel.c::early_init_intel()
> >> - detect_tme()
> >> c->x86_phys_bits -= keyid_bits;
> >
> > Hmm.. Do I read it wrong:
> >
> > static void __init early_identify_cpu(struct cpuinfo_x86 *c)
> > {
> > ...
> > /* cyrix could have cpuid enabled via c_identify()*/
> > if (have_cpuid_p()) {
> > ...
> > // Here we call early_intel_init()
> > if (this_cpu->c_early_init)
> > this_cpu->c_early_init(c);
> > ...
> > }
> >
> > get_cpu_address_sizes(c);
> > ...
> > }
> >
> > ?
> >
> > As far as I see get_cpu_address_sizes() called after early_intel_init().
>
> On `58720809f527 v6.6-rc6 6.6-rc6 2de3c93ef41b' is what I have:
>
> ,----
> | 1599 /* cyrix could have cpuid enabled via c_identify()*/
> | 1600 if (have_cpuid_p()) {
> | 1601 cpu_detect(c);
> | 1602 get_cpu_vendor(c);
> | 1603 get_cpu_cap(c);
> | 1604 get_cpu_address_sizes(c); <= called first
> | 1605 setup_force_cpu_cap(X86_FEATURE_CPUID);
> | 1606 cpu_parse_early_param();
> | 1607
> | 1608 if (this_cpu->c_early_init)
> | 1609 this_cpu->c_early_init(c);
> | 1610
> | 1611 c->cpu_index = 0;
> | 1612 filter_cpuid_features(c, false);
> | 1613
> | 1614 if (this_cpu->c_bsp_init)
> | 1615 this_cpu->c_bsp_init(c);
> | 1616 } else {
> | 1617 setup_clear_cpu_cap(X86_FEATURE_CPUID);
> | 1618 }
> `----
> Listing 1: arch/x86/kernel/cpu/common.c
>
> => get_cpu_address_sizes() is called first which is also conform to my
> experiments and instrumentation.
Ah. It got patched in tip tree. See commit fbf6449f84bf.
--
Kiryl Shutsemau / Kirill A. Shutemov
Powered by blists - more mailing lists