Re: [PATCH] mm/zsmalloc.c: Fix zsmalloc 32-bit PAE support

From: Robin Murphy
Date: Mon Dec 10 2018 - 09:36:07 EST

On 10/12/2018 14:21, Rafael David Tinoco wrote:
On 32-bit systems, zsmalloc uses HIGHMEM and, when PAE is enabled, the
physical frame number might be so big that zsmalloc obj encoding (to
location) will break, causing:

BUG: KASAN: null-ptr-deref in zs_map_object+0xa4/0x2bc
Read of size 4 at addr 00000000 by task mkfs.ext4/623
CPU: 2 PID: 623 Comm: mkfs.ext4 Not tainted 4.19.0-rc8-00017-g8239bc6d3307-dirty #15
Hardware name: Generic DT based system
[<c0418f7c>] (unwind_backtrace) from [<c0410ca4>] (show_stack+0x20/0x24)
[<c0410ca4>] (show_stack) from [<c16bd540>] (dump_stack+0xbc/0xe8)
[<c16bd540>] (dump_stack) from [<c06cab74>] (kasan_report+0x248/0x390)
[<c06cab74>] (kasan_report) from [<c06c94e8>] (__asan_load4+0x78/0xb4)
[<c06c94e8>] (__asan_load4) from [<c06ddc24>] (zs_map_object+0xa4/0x2bc)
[<c06ddc24>] (zs_map_object) from [<bf0bbbd8>] (zram_bvec_rw.constprop.2+0x324/0x8e4 [zram])
[<bf0bbbd8>] (zram_bvec_rw.constprop.2 [zram]) from [<bf0bc3cc>] (zram_make_request+0x234/0x46c [zram])
[<bf0bc3cc>] (zram_make_request [zram]) from [<c09aff9c>] (generic_make_request+0x304/0x63c)
[<c09aff9c>] (generic_make_request) from [<c09b0320>] (submit_bio+0x4c/0x1c8)
[<c09b0320>] (submit_bio) from [<c0743570>] (submit_bh_wbc.constprop.15+0x238/0x26c)
[<c0743570>] (submit_bh_wbc.constprop.15) from [<c0746cf8>] (__block_write_full_page+0x524/0x76c)
[<c0746cf8>] (__block_write_full_page) from [<c07472c4>] (block_write_full_page+0x1bc/0x1d4)
[<c07472c4>] (block_write_full_page) from [<c0748eb4>] (blkdev_writepage+0x24/0x28)
[<c0748eb4>] (blkdev_writepage) from [<c064a780>] (__writepage+0x44/0x78)
[<c064a780>] (__writepage) from [<c064b50c>] (write_cache_pages+0x3b8/0x800)
[<c064b50c>] (write_cache_pages) from [<c064dd78>] (generic_writepages+0x74/0xa0)
[<c064dd78>] (generic_writepages) from [<c0748e64>] (blkdev_writepages+0x18/0x1c)
[<c0748e64>] (blkdev_writepages) from [<c064e890>] (do_writepages+0x68/0x134)
[<c064e890>] (do_writepages) from [<c06368a4>] (__filemap_fdatawrite_range+0xb0/0xf4)
[<c06368a4>] (__filemap_fdatawrite_range) from [<c0636b68>] (file_write_and_wait_range+0x64/0xd0)
[<c0636b68>] (file_write_and_wait_range) from [<c0747af8>] (blkdev_fsync+0x54/0x84)
[<c0747af8>] (blkdev_fsync) from [<c0739dac>] (vfs_fsync_range+0x70/0xd4)
[<c0739dac>] (vfs_fsync_range) from [<c0739e98>] (do_fsync+0x4c/0x80)
[<c0739e98>] (do_fsync) from [<c073a26c>] (sys_fsync+0x1c/0x20)
[<c073a26c>] (sys_fsync) from [<c0401000>] (ret_fast_syscall+0x0/0x2c)

when trying to decode (the pfn) and map the object.

That happens because one architecture might not re-define
MAX_PHYSMEM_BITS, like in this ARM 32-bit w/ LPAE enabled example. For
32-bit systems, if not re-defined, MAX_POSSIBLE_PHYSMEM_BITS will
default to BITS_PER_LONG (32) in most cases, and, with PAE enabled,
_PFN_BITS might be wrong: which may cause obj variable to overflow if
frame number is in HIGHMEM and referencing a page above the 4GB
watermark.

commit 6e00ec00b1a7 ("staging: zsmalloc: calculate MAX_PHYSMEM_BITS if
not defined") realized MAX_PHYSMEM_BITS depended on SPARSEMEM headers
and "fixed" it by calculating it using BITS_PER_LONG if SPARSEMEM wasn't
used, like in the example given above.

Systems with potential for PAE exist for a long time and assuming
BITS_PER_LONG seems inadequate. Defining MAX_PHYSMEM_BITS looks better,
however it is NOT a constant anymore for x86.

SO, instead, MAX_POSSIBLE_PHYSMEM_BITS should be defined by every
architecture using zsmalloc, together with a sanity check for
MAX_POSSIBLE_PHYSMEM_BITS being too big on 32-bit systems.

Link: https://bugs.linaro.org/show_bug.cgi?id=3765#c17
Signed-off-by: Rafael David Tinoco <rafael.tinoco@xxxxxxxxxx>
---
arch/arm/include/asm/pgtable-2level-types.h | 2 ++
arch/arm/include/asm/pgtable-3level-types.h | 2 ++
arch/arm64/include/asm/pgtable-types.h | 2 ++
arch/ia64/include/asm/page.h | 2 ++
arch/mips/include/asm/page.h | 2 ++
arch/powerpc/include/asm/mmu.h | 2 ++
arch/s390/include/asm/page.h | 2 ++
arch/sh/include/asm/page.h | 2 ++
arch/sparc/include/asm/page_32.h | 2 ++
arch/sparc/include/asm/page_64.h | 2 ++
arch/x86/include/asm/pgtable-2level_types.h | 2 ++
arch/x86/include/asm/pgtable-3level_types.h | 3 +-
arch/x86/include/asm/pgtable_64_types.h | 4 +--
mm/zsmalloc.c | 35 +++++++++++----------
14 files changed, 45 insertions(+), 19 deletions(-)

diff --git a/arch/arm/include/asm/pgtable-2level-types.h b/arch/arm/include/asm/pgtable-2level-types.h
index 66cb5b0e89c5..552dba411324 100644
--- a/arch/arm/include/asm/pgtable-2level-types.h
+++ b/arch/arm/include/asm/pgtable-2level-types.h
@@ -64,4 +64,6 @@ typedef pteval_t pgprot_t;
#endif /* STRICT_MM_TYPECHECKS */
+#define MAX_POSSIBLE_PHYSMEM_BITS 32
+
#endif /* _ASM_PGTABLE_2LEVEL_TYPES_H */
diff --git a/arch/arm/include/asm/pgtable-3level-types.h b/arch/arm/include/asm/pgtable-3level-types.h
index 921aa30259c4..664c39e6517c 100644
--- a/arch/arm/include/asm/pgtable-3level-types.h
+++ b/arch/arm/include/asm/pgtable-3level-types.h
@@ -67,4 +67,6 @@ typedef pteval_t pgprot_t;
#endif /* STRICT_MM_TYPECHECKS */
+#define MAX_POSSIBLE_PHYSMEM_BITS 36

Nit: with LPAE, physical addresses go up to 40 bits, not just 36.

Robin.

+
#endif /* _ASM_PGTABLE_3LEVEL_TYPES_H */
diff --git a/arch/arm64/include/asm/pgtable-types.h b/arch/arm64/include/asm/pgtable-types.h
index 345a072b5856..45c3834eb4c8 100644
--- a/arch/arm64/include/asm/pgtable-types.h
+++ b/arch/arm64/include/asm/pgtable-types.h
@@ -64,4 +64,6 @@ typedef struct { pteval_t pgprot; } pgprot_t;
#include <asm-generic/5level-fixup.h>
#endif
+#define MAX_POSSIBLE_PHYSMEM_BITS CONFIG_ARM64_PA_BITS
+
#endif /* __ASM_PGTABLE_TYPES_H */
diff --git a/arch/ia64/include/asm/page.h b/arch/ia64/include/asm/page.h
index 5798bd2b462c..a3e055979e46 100644
--- a/arch/ia64/include/asm/page.h
+++ b/arch/ia64/include/asm/page.h
@@ -235,4 +235,6 @@ get_order (unsigned long size)
#define __HAVE_ARCH_GATE_AREA 1
+#define MAX_POSSIBLE_PHYSMEM_BITS 50
+
#endif /* _ASM_IA64_PAGE_H */
diff --git a/arch/mips/include/asm/page.h b/arch/mips/include/asm/page.h
index e8cc328fce2d..f6a5dea1a66c 100644
--- a/arch/mips/include/asm/page.h
+++ b/arch/mips/include/asm/page.h
@@ -263,4 +263,6 @@ extern int __virt_addr_valid(const volatile void *kaddr);
#include <asm-generic/memory_model.h>
#include <asm-generic/getorder.h>
+#define MAX_POSSIBLE_PHYSMEM_BITS 48
+
#endif /* _ASM_PAGE_H */
diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index eb20eb3b8fb0..2ebc1d2d9a5c 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/arch/powerpc/include/asm/mmu.h
@@ -324,6 +324,8 @@ static inline u16 get_mm_addr_key(struct mm_struct *mm, unsigned long address)
#define MAX_PHYSMEM_BITS 46
#endif
+#define MAX_POSSIBLE_PHYSMEM_BITS MAX_PHYSMEM_BITS
+
#ifdef CONFIG_PPC_BOOK3S_64
#include <asm/book3s/64/mmu.h>
#else /* CONFIG_PPC_BOOK3S_64 */
diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.h
index a4d38092530a..8abec1461bf7 100644
--- a/arch/s390/include/asm/page.h
+++ b/arch/s390/include/asm/page.h
@@ -180,4 +180,6 @@ static inline int devmem_is_allowed(unsigned long pfn)
#include <asm-generic/memory_model.h>
#include <asm-generic/getorder.h>
+#define MAX_POSSIBLE_PHYSMEM_BITS CONFIG_MAX_PHYSMEM_BITS
+
#endif /* _S390_PAGE_H */
diff --git a/arch/sh/include/asm/page.h b/arch/sh/include/asm/page.h
index 5eef8be3e59f..40c7e12cf09e 100644
--- a/arch/sh/include/asm/page.h
+++ b/arch/sh/include/asm/page.h
@@ -205,4 +205,6 @@ typedef struct page *pgtable_t;
#define ARCH_SLAB_MINALIGN 8
#endif
+#define MAX_POSSIBLE_PHYSMEM_BITS 32
+
#endif /* __ASM_SH_PAGE_H */
diff --git a/arch/sparc/include/asm/page_32.h b/arch/sparc/include/asm/page_32.h
index b76d59edec8c..14e9ca4659d7 100644
--- a/arch/sparc/include/asm/page_32.h
+++ b/arch/sparc/include/asm/page_32.h
@@ -139,4 +139,6 @@ extern unsigned long pfn_base;
#include <asm-generic/memory_model.h>
#include <asm-generic/getorder.h>
+#define MAX_POSSIBLE_PHYSMEM_BITS 32
+
#endif /* _SPARC_PAGE_H */
diff --git a/arch/sparc/include/asm/page_64.h b/arch/sparc/include/asm/page_64.h
index e80f2d5bf62f..6d6f3654ead1 100644
--- a/arch/sparc/include/asm/page_64.h
+++ b/arch/sparc/include/asm/page_64.h
@@ -163,4 +163,6 @@ extern unsigned long PAGE_OFFSET;
#include <asm-generic/getorder.h>
+#define MAX_POSSIBLE_PHYSMEM_BITS MAX_PHYS_ADDRESS_BITS
+
#endif /* _SPARC64_PAGE_H */
diff --git a/arch/x86/include/asm/pgtable-2level_types.h b/arch/x86/include/asm/pgtable-2level_types.h
index 6deb6cd236e3..c2eae59e6505 100644
--- a/arch/x86/include/asm/pgtable-2level_types.h
+++ b/arch/x86/include/asm/pgtable-2level_types.h
@@ -38,4 +38,6 @@ typedef union {
/* This covers all VMSPLIT_* and VMSPLIT_*_OPT variants */
#define PGD_KERNEL_START (CONFIG_PAGE_OFFSET >> PGDIR_SHIFT)
+#define MAX_POSSIBLE_PHYSMEM_BITS 32
+
#endif /* _ASM_X86_PGTABLE_2LEVEL_DEFS_H */
diff --git a/arch/x86/include/asm/pgtable-3level_types.h b/arch/x86/include/asm/pgtable-3level_types.h
index 33845d36897c..5fce514a49a0 100644
--- a/arch/x86/include/asm/pgtable-3level_types.h
+++ b/arch/x86/include/asm/pgtable-3level_types.h
@@ -45,7 +45,8 @@ typedef union {
*/
#define PTRS_PER_PTE 512
-#define MAX_POSSIBLE_PHYSMEM_BITS 36
#define PGD_KERNEL_START (CONFIG_PAGE_OFFSET >> PGDIR_SHIFT)
+#define MAX_POSSIBLE_PHYSMEM_BITS 36
+
#endif /* _ASM_X86_PGTABLE_3LEVEL_DEFS_H */
diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
index 84bd9bdc1987..d808cfde3d19 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -64,8 +64,6 @@ extern unsigned int ptrs_per_p4d;
#define P4D_SIZE (_AC(1, UL) << P4D_SHIFT)
#define P4D_MASK (~(P4D_SIZE - 1))
-#define MAX_POSSIBLE_PHYSMEM_BITS 52
-
#else /* CONFIG_X86_5LEVEL */
/*
@@ -154,4 +152,6 @@ extern unsigned int ptrs_per_p4d;
#define PGD_KERNEL_START ((PAGE_SIZE / 2) / sizeof(pgd_t))
+#define MAX_POSSIBLE_PHYSMEM_BITS (pgtable_l5_enabled() ? 52 : 46)
+
#endif /* _ASM_X86_PGTABLE_64_DEFS_H */
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 0787d33b80d8..132c20b6fd4f 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -80,23 +80,7 @@
* as single (unsigned long) handle value.
*
* Note that object index <obj_idx> starts from 0.
- *
- * This is made more complicated by various memory models and PAE.
- */
-
-#ifndef MAX_POSSIBLE_PHYSMEM_BITS
-#ifdef MAX_PHYSMEM_BITS
-#define MAX_POSSIBLE_PHYSMEM_BITS MAX_PHYSMEM_BITS
-#else
-/*
- * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just
- * be PAGE_SHIFT
*/
-#define MAX_POSSIBLE_PHYSMEM_BITS BITS_PER_LONG
-#endif
-#endif
-
-#define _PFN_BITS (MAX_POSSIBLE_PHYSMEM_BITS - PAGE_SHIFT)
/*
* Memory for allocating for handle keeps object position by
@@ -116,6 +100,25 @@
*/
#define OBJ_ALLOCATED_TAG 1
#define OBJ_TAG_BITS 1
+
+/*
+ * MAX_POSSIBLE_PHYSMEM_BITS should be defined by all archs using zsmalloc:
+ * Trying to guess it from MAX_PHYSMEM_BITS, or considering it BITS_PER_LONG,
+ * proved to be wrong by not considering PAE capabilities, or using SPARSEMEM
+ * only headers, leading to bad object encoding due to object index overflow.
+ */
+#ifndef MAX_POSSIBLE_PHYSMEM_BITS
+ #define MAX_POSSIBLE_PHYSMEM_BITS BITS_PER_LONG
+ #error "MAX_POSSIBLE_PHYSMEM_BITS HAS to be defined by arch using zsmalloc";
+#else
+ #ifndef CONFIG_64BIT
+ #if (MAX_POSSIBLE_PHYSMEM_BITS >= (BITS_PER_LONG + PAGE_SHIFT - OBJ_TAG_BITS))
+ #error "MAX_POSSIBLE_PHYSMEM_BITS is wrong for this arch";
+ #endif
+ #endif
+#endif
+
+#define _PFN_BITS (MAX_POSSIBLE_PHYSMEM_BITS - PAGE_SHIFT)
#define OBJ_INDEX_BITS (BITS_PER_LONG - _PFN_BITS - OBJ_TAG_BITS)
#define OBJ_INDEX_MASK ((_AC(1, UL) << OBJ_INDEX_BITS) - 1)