[PATCH] sparc32: Fix pgd lookup in vmalloc fault handling

[Ludwig Rydberg]

Check and synchronize the level-1 entry with the PUD accessors instead
of the PGD ones. SPARC32 folds the P4D and PUD levels into the PGD and
pgd_present() always returns 1. The PGD accessors therefore skipped the
synchronization and the handler dereferenced a PMD pointer derived from
the missing entry (seen in this kernel panic running v5.10.194):

  Unable to handle kernel paging request at virtual address ff780000
  PC: <do_sparc_fault+0x20c/0x3c8>
  Caller[f0007ed4]: srmmu_fault+0x60/0x70

  do_sparc_fault+0x20c/0x3c8:
    pmd_present at arch/sparc/include/asm/pgtable_32.h:193
    (inlined by) do_sparc_fault at arch/sparc/mm/fault_32.c:358

Fixes: 7235db268a27 ("sparc32: use pgtable-nopud instead of 4level-fixup")
Signed-off-by: Ludwig Rydberg <ludwig.rydberg@xxxxxxxxxxx>
---
 arch/sparc/mm/fault_32.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/sparc/mm/fault_32.c b/arch/sparc/mm/fault_32.c
index 86a831ebd8c8..f9befdbb3e72 100644
--- a/arch/sparc/mm/fault_32.c
+++ b/arch/sparc/mm/fault_32.c
@@ -276,21 +276,21 @@ asmlinkage void do_sparc_fault(struct pt_regs *regs, int text_fault, int write,
 		pmd_t *pmd, *pmd_k;
 
 		pgd = tsk->active_mm->pgd + offset;
+		p4d = p4d_offset(pgd, address);
+		pud = pud_offset(p4d, address);
+
 		pgd_k = init_mm.pgd + offset;
+		p4d_k = p4d_offset(pgd_k, address);
+		pud_k = pud_offset(p4d_k, address);
 
-		if (!pgd_present(*pgd)) {
-			if (!pgd_present(*pgd_k))
+		if (!pud_present(*pud)) {
+			if (!pud_present(*pud_k))
 				goto bad_area_nosemaphore;
-			pgd_val(*pgd) = pgd_val(*pgd_k);
+			pud_val(*pud) = pud_val(*pud_k);
 			return;
 		}
 
-		p4d = p4d_offset(pgd, address);
-		pud = pud_offset(p4d, address);
 		pmd = pmd_offset(pud, address);
-
-		p4d_k = p4d_offset(pgd_k, address);
-		pud_k = pud_offset(p4d_k, address);
 		pmd_k = pmd_offset(pud_k, address);
 
 		if (pmd_present(*pmd) || !pmd_present(*pmd_k))

base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
-- 
2.35.3