Commit 545ac14c authored by Joerg Roedel's avatar Joerg Roedel Committed by Borislav Petkov
Browse files

x86/sev-es: Check regs->sp is trusted before adjusting #VC IST stack 



The code in the NMI handler to adjust the #VC handler IST stack is
needed in case an NMI hits when the #VC handler is still using its IST
stack.

But the check for this condition also needs to look if the regs->sp
value is trusted, meaning it was not set by user-space. Extend the check
to not use regs->sp when the NMI interrupted user-space code or the
SYSCALL gap.

Fixes: 315562c9 ("x86/sev-es: Adjust #VC IST Stack on entering NMI handler")
Reported-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org # 5.10+
Link: https://lkml.kernel.org/r/20210303141716.29223-3-joro@8bytes.org
parent 78a81d88

arch/x86/kernel/sev-es.c

+12 −2
Original line number Diff line number Diff line
@@ -121,8 +121,18 @@ static void __init setup_vc_stacks(int cpu) 
	cea_set_pte((void *)vaddr, pa, PAGE_KERNEL);

}



static __always_inline bool on_vc_stack(unsigned long sp)

static __always_inline bool on_vc_stack(struct pt_regs *regs)

{

	unsigned long sp = regs->sp;



	/* User-mode RSP is not trusted */

	if (user_mode(regs))

		return false;



	/* SYSCALL gap still has user-mode RSP */

	if (ip_within_syscall_gap(regs))

		return false;



	return ((sp >= __this_cpu_ist_bottom_va(VC)) && (sp < __this_cpu_ist_top_va(VC)));

}
@@ -144,7 +154,7 @@ void noinstr __sev_es_ist_enter(struct pt_regs *regs) 
	old_ist = __this_cpu_read(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC]);



	/* Make room on the IST stack */

	if (on_vc_stack(regs->sp))

	if (on_vc_stack(regs))

		new_ist = ALIGN_DOWN(regs->sp, 8) - sizeof(old_ist);

	else

		new_ist = old_ist - sizeof(old_ist);