⬢ DragonFlyBSD Kernel Audit
DF-5155 / pbfix.c
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/*
 * DF-5155 fix-path replica — implements perfbias_set_handler() exactly as
 * after fix.diff (wrmsr_safe/rdmsr_safe + error propagation). Loading this
 * on the patched kernel demonstrates the post-fix instruction sequence on
 * the same platform where the baseline raw wrmsr took Fatal trap 9:
 * expected "wrmsr_safe -> error 14" and NO trap.
 */
#include <sys/param.h>
#include <sys/module.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <machine/cpufunc.h>

#define INTEL_MSR_PERF_BIAS	0x1b0

static int
pbfix_modevent(module_t mod, int type, void *data)
{
	uint64_t val = 0;
	int error;

	switch (type) {
	case MOD_LOAD:
		/* the patched perfbias_set_handler body, verbatim shape */
		error = wrmsr_safe(INTEL_MSR_PERF_BIAS, 7);
		if (error == 0) {
			val = rdmsr(INTEL_MSR_PERF_BIAS);
			kprintf("pbfix: hint now %#llx\n",
			    (unsigned long long)(val & 0xf));
		}
		kprintf("pbfix: patched handler returns error %d "
		    "(sysctl writer gets EIO, no trap)\n", error);
		return 0;
	case MOD_UNLOAD:
		return 0;
	}
	return EOPNOTSUPP;
}

static moduledata_t pbfix_mod = {
	"pbfix",
	pbfix_modevent,
	NULL
};

DECLARE_MODULE(pbfix, pbfix_mod, SI_SUB_DRIVERS, SI_ORDER_ANY);