In the Linux kernel, the following vulnerability has been resolved:
x86/fpu: Invalidate FPU state after a failed XRSTOR from a user buffer
Both Intel and AMD consider it to be architecturally valid for XRSTOR to
fail with #PF but nonetheless change the register state. The actual
conditions under which this might occur are unclear [1], but it seems
plausible that this might be triggered if one sibling thread unmaps a page
and invalidates the shared TLB while another sibling thread is executing
XRSTOR on the page in question.
__fpu__restore_sig() can execute XRSTOR while the hardware registers
are preserved on behalf of a different victim task (using the
fpu_fpregs_owner_ctx mechanism), and, in theory, XRSTOR could fail but
modify the registers.
If this happens, then there is a window in which __fpu__restore_sig()
could schedule out and the victim task could schedule back in without
reloading its own FPU registers. This would result in part of the FPU
state that __fpu__restore_sig() was attempting to load leaking into the
victim task’s user-visible state.
Invalidate preserved FPU registers on XRSTOR failure to prevent this
situation from corrupting any state.
[1] Frequent readers of the errata lists might imagine “complex
microarchitectural conditions”.
[
{
"product": "Linux",
"vendor": "Linux",
"defaultStatus": "unaffected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"programFiles": [
"arch/x86/kernel/fpu/signal.c"
],
"versions": [
{
"version": "1d731e731c4c",
"lessThan": "a7748e021b9f",
"status": "affected",
"versionType": "git"
},
{
"version": "1d731e731c4c",
"lessThan": "002665dcba4b",
"status": "affected",
"versionType": "git"
},
{
"version": "1d731e731c4c",
"lessThan": "d8778e393afa",
"status": "affected",
"versionType": "git"
}
]
},
{
"product": "Linux",
"vendor": "Linux",
"defaultStatus": "affected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"programFiles": [
"arch/x86/kernel/fpu/signal.c"
],
"versions": [
{
"version": "5.2",
"status": "affected"
},
{
"version": "0",
"lessThan": "5.2",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "5.10.46",
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "5.12.13",
"lessThanOrEqual": "5.12.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "5.13",
"lessThanOrEqual": "*",
"status": "unaffected",
"versionType": "original_commit_for_fix"
}
]
}
]