We failed to activate the mitigation for Spectre-RSB (Return Stack
Buffer, aka. ret2spec) on context switch, on CPUs prior to Power9
DD2.3.
That allows a process to poison the RSB (called Link Stack on Power
CPUs) and possibly misdirect speculative execution of another process.
If the victim process can be induced to execute a leak gadget then it
may be possible to extract information from the victim via a side
channel.
The fix is to correctly activate the link stack flush mitigation on
all CPUs that have any mitigation of Spectre v2 in userspace enabled.
There's a second commit which adds a link stack flush in the KVM guest
exit path. A leak via that path has not been demonstrated, but we
believe it's at least theoretically possible.
This is the fix for CVE-2019-18660.
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Merge tag 'powerpc-spectre-rsb' of powerpc-CVE-2019-18660.bundle
Pull powerpc Spectre-RSB fixes from Michael Ellerman:
"We failed to activate the mitigation for Spectre-RSB (Return Stack
Buffer, aka. ret2spec) on context switch, on CPUs prior to Power9
DD2.3.
That allows a process to poison the RSB (called Link Stack on Power
CPUs) and possibly misdirect speculative execution of another process.
If the victim process can be induced to execute a leak gadget then it
may be possible to extract information from the victim via a side
channel.
The fix is to correctly activate the link stack flush mitigation on
all CPUs that have any mitigation of Spectre v2 in userspace enabled.
There's a second commit which adds a link stack flush in the KVM guest
exit path. A leak via that path has not been demonstrated, but we
believe it's at least theoretically possible.
This is the fix for CVE-2019-18660"
* tag 'powerpc-spectre-rsb' of /home/torvalds/Downloads/powerpc-CVE-2019-18660.bundle:
KVM: PPC: Book3S HV: Flush link stack on guest exit to host kernel
powerpc/book3s64: Fix link stack flush on context switch
80eb5fea3c