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From:   Qian Cai <cai@lca.pw>
To:     mpe@ellerman.id.au, akpm@linux-foundation.org
Cc:     rashmicy@gmail.com, christophe.leroy@c-s.fr, linux-mm@kvack.org,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        Qian Cai <cai@lca.pw>
Subject: [PATCH -next v2] powerpc/64s/pgtable: fix an undefined behaviour
Date:   Thu,  5 Mar 2020 09:32:39 -0500
Message-Id: <1583418759-16105-1-git-send-email-cai@lca.pw>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Booting a power9 server with hash MMU could trigger an undefined
behaviour because pud_offset(p4d, 0) will do,

0 >> (PAGE_SHIFT:16 + PTE_INDEX_SIZE:8 + H_PMD_INDEX_SIZE:10)

Fix it by converting pud_offset() and friends to static inline
functions.

 UBSAN: shift-out-of-bounds in arch/powerpc/mm/ptdump/ptdump.c:282:15
 shift exponent 34 is too large for 32-bit type 'int'
 CPU: 6 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc4-next-20200303+ #13
 Call Trace:
 dump_stack+0xf4/0x164 (unreliable)
 ubsan_epilogue+0x18/0x78
 __ubsan_handle_shift_out_of_bounds+0x160/0x21c
 walk_pagetables+0x2cc/0x700
 walk_pud at arch/powerpc/mm/ptdump/ptdump.c:282
 (inlined by) walk_pagetables at arch/powerpc/mm/ptdump/ptdump.c:311
 ptdump_check_wx+0x8c/0xf0
 mark_rodata_ro+0x48/0x80
 kernel_init+0x74/0x194
 ret_from_kernel_thread+0x5c/0x74

Suggested-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Qian Cai <cai@lca.pw>
---
 arch/powerpc/include/asm/book3s/64/pgtable.h | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index fa60e8594b9f..4967bc9e25e2 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -1016,12 +1016,20 @@ static inline bool p4d_access_permitted(p4d_t p4d, bool write)
 
 #define pgd_offset(mm, address)	 ((mm)->pgd + pgd_index(address))
 
-#define pud_offset(p4dp, addr)	\
-	(((pud_t *) p4d_page_vaddr(*(p4dp))) + pud_index(addr))
-#define pmd_offset(pudp,addr) \
-	(((pmd_t *) pud_page_vaddr(*(pudp))) + pmd_index(addr))
-#define pte_offset_kernel(dir,addr) \
-	(((pte_t *) pmd_page_vaddr(*(dir))) + pte_index(addr))
+static inline pud_t *pud_offset(p4d_t *p4d, unsigned long address)
+{
+	return (pud_t *)p4d_page_vaddr(*p4d) + pud_index(address);
+}
+
+static inline pmd_t *pmd_offset(pud_t *pud, unsigned long address)
+{
+	return (pmd_t *)pud_page_vaddr(*pud) + pmd_index(address);
+}
+
+static inline pte_t *pte_offset_kernel(pmd_t *pmd, unsigned long address)
+{
+	return (pte_t *)pmd_page_vaddr(*pmd) + pte_index(address);
+}
 
 #define pte_offset_map(dir,addr)	pte_offset_kernel((dir), (addr))
 
-- 
1.8.3.1