[PATCH 5.5 084/367] powerpc/ptdump: Fix W+X verification

Greg Kroah-Hartman
2020-02-10T13:06:33Z

From: Christophe Leroy <christophe.leroy@c-s.fr>

commit d80ae83f1f932ab7af47b54d0d3bef4f4dba489f upstream.

Verification cannot rely on simple bit checking because on some
platforms PAGE_RW is 0, checking that a page is not W means
checking that PAGE_RO is set instead of checking that PAGE_RW
is not set.

Use pte helpers instead of checking bits.

Fixes: 453d87f6a8ae ("powerpc/mm: Warn if W+X pages found on boot")
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0d894839fdbb19070f0e1e4140363be4f2bb62fc.1578989540.git.christophe.leroy@c-s.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/mm/ptdump/ptdump.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/powerpc/mm/ptdump/ptdump.c
+++ b/arch/powerpc/mm/ptdump/ptdump.c
@@ -173,10 +173,12 @@ static void dump_addr(struct pg_state *s

static void note_prot_wx(struct pg_state *st, unsigned long addr)
{
+ pte_t pte = __pte(st->current_flags);
+
if (!IS_ENABLED(CONFIG_PPC_DEBUG_WX) || !st->check_wx)
return;

- if (!((st->current_flags & pgprot_val(PAGE_KERNEL_X)) == pgprot_val(PAGE_KERNEL_X)))
+ if (!pte_write(pte) || !pte_exec(pte))
return;

WARN_ONCE(1, "powerpc/mm: Found insecure W+X mapping at address %p/%pS\n",