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Subject[PATCH 4.18 192/197] x86/xen: dont write ptes directly in 32-bit PV guests
Date
4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Juergen Gross <jgross@suse.com>

commit f7c90c2aa4004808dff777ba6ae2c7294dd06851 upstream.

In some cases 32-bit PAE PV guests still write PTEs directly instead of
using hypercalls. This is especially bad when clearing a PTE as this is
done via 32-bit writes which will produce intermediate L1TF attackable
PTEs.

Change the code to use hypercalls instead.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/xen/mmu_pv.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -434,14 +434,13 @@ static void xen_set_pud(pud_t *ptr, pud_
static void xen_set_pte_atomic(pte_t *ptep, pte_t pte)
{
trace_xen_mmu_set_pte_atomic(ptep, pte);
- set_64bit((u64 *)ptep, native_pte_val(pte));
+ __xen_set_pte(ptep, pte);
}

static void xen_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
{
trace_xen_mmu_pte_clear(mm, addr, ptep);
- if (!xen_batched_set_pte(ptep, native_make_pte(0)))
- native_pte_clear(mm, addr, ptep);
+ __xen_set_pte(ptep, native_make_pte(0));
}

static void xen_pmd_clear(pmd_t *pmdp)
@@ -1571,7 +1570,7 @@ static void __init xen_set_pte_init(pte_
pte = __pte_ma(((pte_val_ma(*ptep) & _PAGE_RW) | ~_PAGE_RW) &
pte_val_ma(pte));
#endif
- native_set_pte(ptep, pte);
+ __xen_set_pte(ptep, pte);
}

/* Early in boot, while setting up the initial pagetable, assume

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