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| author | Jane Malalane <jane.malalane@citrix.com> | 2021-10-21 12:47:44 +0200 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2021-10-21 20:49:16 +0200 |
| commit | 415de44076640483648d6c0f6d645a9ee61328ad (patch) | |
| tree | 73413514d8731a52b6e460589f7ae12c1c2dbff2 /arch/x86/kernel/cpu/hygon.c | |
| parent | x86/CPU: Add support for Vortex CPUs (diff) | |
| download | linux-415de44076640483648d6c0f6d645a9ee61328ad.tar.xz linux-415de44076640483648d6c0f6d645a9ee61328ad.zip | |
x86/cpu: Fix migration safety with X86_BUG_NULL_SEL
Currently, Linux probes for X86_BUG_NULL_SEL unconditionally which
makes it unsafe to migrate in a virtualised environment as the
properties across the migration pool might differ.
To be specific, the case which goes wrong is:
1. Zen1 (or earlier) and Zen2 (or later) in a migration pool
2. Linux boots on Zen2, probes and finds the absence of X86_BUG_NULL_SEL
3. Linux is then migrated to Zen1
Linux is now running on a X86_BUG_NULL_SEL-impacted CPU while believing
that the bug is fixed.
The only way to address the problem is to fully trust the "no longer
affected" CPUID bit when virtualised, because in the above case it would
be clear deliberately to indicate the fact "you might migrate to
somewhere which has this behaviour".
Zen3 adds the NullSelectorClearsBase CPUID bit to indicate that loading
a NULL segment selector zeroes the base and limit fields, as well as
just attributes. Zen2 also has this behaviour but doesn't have the NSCB
bit.
[ bp: Minor touchups. ]
Signed-off-by: Jane Malalane <jane.malalane@citrix.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
CC: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20211021104744.24126-1-jane.malalane@citrix.com
Diffstat (limited to 'arch/x86/kernel/cpu/hygon.c')
| -rw-r--r-- | arch/x86/kernel/cpu/hygon.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/x86/kernel/cpu/hygon.c b/arch/x86/kernel/cpu/hygon.c index 6d50136f7ab9..3fcdda4c1e11 100644 --- a/arch/x86/kernel/cpu/hygon.c +++ b/arch/x86/kernel/cpu/hygon.c @@ -335,6 +335,8 @@ static void init_hygon(struct cpuinfo_x86 *c) /* Hygon CPUs don't reset SS attributes on SYSRET, Xen does. */ if (!cpu_has(c, X86_FEATURE_XENPV)) set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS); + + check_null_seg_clears_base(c); } static void cpu_detect_tlb_hygon(struct cpuinfo_x86 *c) |