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x86/cpu: Adjust enable_nmis() to be shadow stack compatible
When executing an IRET-to-self, the shadow stack must agree with the regular stack. We can't manipulate SSP directly, so have to fake a shadow IRET frame by executing 3 CALLs, then editing the result to look correct. This is not a fastpath, is called on the BSP long before CET can be set up, and may be called on the crash path after CET is disabled. Use the fact that INCSSP is allocated from the hint nop space to construct a test for CET being active which is safe on all processors. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com>
This commit is contained in:
Andrew Cooper committed
1 parent
91d26ed304
commit
e952f1d67b
1 file changed
+33
-10
@@ -550,17 +550,40 @@ static inline void enable_nmis(void)
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{
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unsigned long tmp;
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asm volatile ( "mov %%rsp, %[tmp] \n\t"
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"push %[ss] \n\t"
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"push %[tmp] \n\t"
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"pushf \n\t"
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"push %[cs] \n\t"
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"lea 1f(%%rip), %[tmp] \n\t"
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"push %[tmp] \n\t"
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"iretq; 1: \n\t"
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: [tmp] "=&r" (tmp)
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asm volatile ( "mov %%rsp, %[rsp] \n\t"
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"lea .Ldone(%%rip), %[rip] \n\t"
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#ifdef CONFIG_XEN_SHSTK
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/* Check for CET-SS being active. */
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"mov $1, %k[ssp] \n\t"
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"rdsspq %[ssp] \n\t"
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"cmp $1, %k[ssp] \n\t"
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"je .Lshstk_done \n\t"
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/* Push 3 words on the shadow stack */
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".rept 3 \n\t"
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"call 1f; nop; 1: \n\t"
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".endr \n\t"
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/* Fixup to be an IRET shadow stack frame */
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"wrssq %q[cs], -1*8(%[ssp]) \n\t"
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"wrssq %[rip], -2*8(%[ssp]) \n\t"
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"wrssq %[ssp], -3*8(%[ssp]) \n\t"
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".Lshstk_done:"
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#endif
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/* Write an IRET regular frame */
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"push %[ss] \n\t"
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"push %[rsp] \n\t"
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"pushf \n\t"
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"push %q[cs] \n\t"
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"push %[rip] \n\t"
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"iretq \n\t"
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".Ldone: \n\t"
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: [rip] "=&r" (tmp),
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[rsp] "=&r" (tmp),
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[ssp] "=&r" (tmp)
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: [ss] "i" (__HYPERVISOR_DS),
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[cs] "i" (__HYPERVISOR_CS) );
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[cs] "r" (__HYPERVISOR_CS) );
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}
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void sysenter_entry(void);
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