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amd64: do not enable PKRU if user disabled saving PKRU register in xsave mask

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This is done by reverting CR4_PKE bit, because we perform %CR4
initialization in initializecpu(), and the function is called before
xsave_mask is read.  To not redo the whole early initialization
sequence for the corner case, this should be good enough.

Reported by:	jhb
Reviewed by:	jhb, markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D38219
This commit is contained in:
Konstantin Belousov 2023-01-27 12:45:02 +02:00
parent 11989314dc
commit 153643a5bc
1 changed files with 17 additions and 1 deletions
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18
sys/amd64/amd64/fpu.c
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@ -372,6 +372,7 @@ void
fpuinit(void)
{
register_t saveintr;
uint64_t cr4;
u_int mxcsr;
u_short control;
@ -379,7 +380,22 @@ fpuinit(void)
fpuinit_bsp1();
if (use_xsave) {
load_cr4(rcr4() | CR4_XSAVE);
cr4 = rcr4();
/*
* Revert enablement of PKRU if user disabled its
* saving on context switches by clearing the bit in
* the xsave mask. Also redundantly clear the bit in
* cpu_stdext_feature2 to prevent pmap from ever
* trying to set the page table bits.
*/
if ((cpu_stdext_feature2 & CPUID_STDEXT2_PKU) != 0 &&
(xsave_mask & XFEATURE_ENABLED_PKRU) == 0) {
cr4 &= ~CR4_PKE;
cpu_stdext_feature2 &= ~CPUID_STDEXT2_PKU;
}
load_cr4(cr4 | CR4_XSAVE);
load_xcr(XCR0, xsave_mask);
}