linux-kernel - [PATCH v3] powerpc/64s/pgtable: fix an undefined behaviour

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Message-Id: <20200306044852.3236-1-cai@lca.pw>
Date:   Thu,  5 Mar 2020 23:48:52 -0500
From:   Qian Cai <cai@....pw>
To:     mpe@...erman.id.au
Cc:     rashmicy@...il.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Qian Cai <cai@....pw>,
        Christophe Leroy <christophe.leroy@....fr>
Subject: [PATCH v3] powerpc/64s/pgtable: fix an undefined behaviour

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_index() 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@....fr>
Signed-off-by: Qian Cai <cai@....pw>
---

v3: convert pud_index() etc to static inline functions.
v2: convert pud_offset() etc to static inline functions.

 arch/powerpc/include/asm/book3s/64/pgtable.h | 23 ++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 201a69e6a355..bd432c6706b9 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -998,10 +998,25 @@ extern struct page *pgd_page(pgd_t pgd);
 #define pud_page_vaddr(pud)	__va(pud_val(pud) & ~PUD_MASKED_BITS)
 #define pgd_page_vaddr(pgd)	__va(pgd_val(pgd) & ~PGD_MASKED_BITS)
 
-#define pgd_index(address) (((address) >> (PGDIR_SHIFT)) & (PTRS_PER_PGD - 1))
-#define pud_index(address) (((address) >> (PUD_SHIFT)) & (PTRS_PER_PUD - 1))
-#define pmd_index(address) (((address) >> (PMD_SHIFT)) & (PTRS_PER_PMD - 1))
-#define pte_index(address) (((address) >> (PAGE_SHIFT)) & (PTRS_PER_PTE - 1))
+static inline unsigned long pgd_index(unsigned long address)
+{
+	return (address >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1);
+}
+
+static inline unsigned long pud_index(unsigned long address)
+{
+	return (address >> PUD_SHIFT) & (PTRS_PER_PUD - 1);
+}
+
+static inline unsigned long pmd_index(unsigned long address)
+{
+	return (address >> PMD_SHIFT) & (PTRS_PER_PMD - 1);
+}
+
+static inline unsigned long pte_index(unsigned long address)
+{
+	return (address >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
+}
 
 /*
  * Find an entry in a page-table-directory.  We combine the address region
-- 
2.21.0 (Apple Git-122.2)