x86, realmode: Mask out EFER.LMA when saving trampoline EFER (79603879) · Commits · 戴 / test

Some AMD processors apparently #GP(0) if EFER.LMA is set in WRMSR, rather than ignoring it. Thus, we need to mask it out. Reported-by:

Borislav Petkov <bp@alien8.de> Cc: Jarkko Sakkinen <jarkko.sakkinen@intel.com> Signed-off-by:

arch/x86/kernel/realmode.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -22,6 +22,7 @@ void __init setup_real_mode(void)
		size_t size = PAGE_ALIGN(real_mode_blob_end - real_mode_blob);
		#ifdef CONFIG_X86_64
		u64 *trampoline_pgd;
		u32 efer_low, efer_high;
		#endif

		/* Has to be in very low memory so we can execute real-mode AP code. */
		@@ -65,9 +66,13 @@ void __init setup_real_mode(void)
		trampoline_header->gdt_limit = __BOOT_DS + 7;
		trampoline_header->gdt_base = __pa(boot_gdt);
		#else
		if (rdmsr_safe(MSR_EFER, &trampoline_header->efer_low,
		&trampoline_header->efer_high))
		BUG();
		/*
		* Some AMD processors will #GP(0) if EFER.LMA is set in WRMSR
		* so we need to mask it out.
		*/
		rdmsr(MSR_EFER, efer_low, efer_high);
		trampoline_header->efer_low = efer_low & ~EFER_LMA;
		trampoline_header->efer_high = efer_high;

		trampoline_header->start = (u64) secondary_startup_64;
		trampoline_cr4_features = &trampoline_header->cr4;