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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: 315562c9af ("x86/sev-es: Adjust #VC IST Stack on entering NMI handler")
Reported-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org # 5.10+
Link: https://lkml.kernel.org/r/20210303141716.29223-3-joro@8bytes.org
This commit is contained in:
Joerg Roedel 2021-03-03 15:17:13 +01:00 committed by Borislav Petkov
parent 78a81d88f6
commit 545ac14c16
1 changed files with 12 additions and 2 deletions
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14
arch/x86/kernel/sev-es.c
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@ -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);