* [PATCH 1 of 2] Fix invalid memory access in OCaml mmap library (to play nicely with the GC)
2011-09-30 15:39 [PATCH 0 of 2] Invalid memory access in OCaml mmap library Zheng Li
@ 2011-09-30 15:39 ` Zheng Li
2011-09-30 16:34 ` Ian Campbell
2011-10-06 16:47 ` Ian Jackson
2011-09-30 15:40 ` [PATCH 2 of 2] Change GET_C_STRUCT to Intf_val to follow the common naming scheme of OCaml macro Zheng Li
1 sibling, 2 replies; 6+ messages in thread
From: Zheng Li @ 2011-09-30 15:39 UTC (permalink / raw)
To: xen-devel
[-- Attachment #1: Type: text/plain, Size: 3404 bytes --]
This was a bug reported by Roberto Di Cosmo. When he tried to reuse the mmap library for his own project, Mmap.read occasionally got different result when reading from the same map. This turned out to be a bug in the binding, where a C pointer was created pointing to a OCaml value, and the OCaml value was subsequently moved around by the GC after memory allocation and hence invalidated the C pointer. This patch removes the indirection of C pointer and uses OCaml macro to access values directly.
Only Mmap.read function had this problem. The other functions, despite having the same code style, didn't have memory allocation involved hence wouldn't intrigue such an error. I've changed all of them to the safer style for future proof. Directly casting OCaml value's *data block* (rather than the value itself) as a C pointer is not a common practice either, but I'll leave it as it is.
The bug hadn't occured on XenServer because XenServer didn't make use of the Mmap.read function (except in one place for debugging). In XenServer, most mmap operations were going through another pair of separately implemented functions (Xs_ring.read/write).
Signed-off-by: Zheng Li <dev@zheng.li>
tools/ocaml/libs/mmap/mmap_stubs.c | 24 +++++++++---------------
1 files changed, 9 insertions(+), 15 deletions(-)
----
diff --git a/tools/ocaml/libs/mmap/mmap_stubs.c b/tools/ocaml/libs/mmap/mmap_stubs.c
--- a/tools/ocaml/libs/mmap/mmap_stubs.c
+++ b/tools/ocaml/libs/mmap/mmap_stubs.c
@@ -71,12 +71,10 @@ CAMLprim value stub_mmap_init(value fd,
CAMLprim value stub_mmap_final(value interface)
{
CAMLparam1(interface);
- struct mmap_interface *intf;
- intf = GET_C_STRUCT(interface);
- if (intf->addr != MAP_FAILED)
- munmap(intf->addr, intf->len);
- intf->addr = MAP_FAILED;
+ if (GET_C_STRUCT(interface)->addr != MAP_FAILED)
+ munmap(GET_C_STRUCT(interface)->addr, GET_C_STRUCT(interface)->len);
+ GET_C_STRUCT(interface)->addr = MAP_FAILED;
CAMLreturn(Val_unit);
}
@@ -85,21 +83,19 @@ CAMLprim value stub_mmap_read(value inte
{
CAMLparam3(interface, start, len);
CAMLlocal1(data);
- struct mmap_interface *intf;
int c_start;
int c_len;
c_start = Int_val(start);
c_len = Int_val(len);
- intf = GET_C_STRUCT(interface);
- if (c_start > intf->len)
+ if (c_start > GET_C_STRUCT(interface)->len)
caml_invalid_argument("start invalid");
- if (c_start + c_len > intf->len)
+ if (c_start + c_len > GET_C_STRUCT(interface)->len)
caml_invalid_argument("len invalid");
data = caml_alloc_string(c_len);
- memcpy((char *) data, intf->addr + c_start, c_len);
+ memcpy((char *) data, GET_C_STRUCT(interface)->addr + c_start, c_len);
CAMLreturn(data);
}
@@ -108,20 +104,18 @@ CAMLprim value stub_mmap_write(value int
value start, value len)
{
CAMLparam4(interface, data, start, len);
- struct mmap_interface *intf;
int c_start;
int c_len;
c_start = Int_val(start);
c_len = Int_val(len);
- intf = GET_C_STRUCT(interface);
- if (c_start > intf->len)
+ if (c_start > GET_C_STRUCT(interface)->len)
caml_invalid_argument("start invalid");
- if (c_start + c_len > intf->len)
+ if (c_start + c_len > GET_C_STRUCT(interface)->len)
caml_invalid_argument("len invalid");
- memcpy(intf->addr + c_start, (char *) data, c_len);
+ memcpy(GET_C_STRUCT(interface)->addr + c_start, (char *) data, c_len);
CAMLreturn(Val_unit);
}
[-- Attachment #2: xen-unstable.hg-1.patch --]
[-- Type: text/x-patch, Size: 3278 bytes --]
This was a bug reported by Roberto Di Cosmo. When he tried to reuse the mmap library for his own project, Mmap.read occasionally got different result when reading from the same map. This turned out to be a bug in the binding, where a C pointer was created pointing to a OCaml value, and the OCaml value was subsequently moved around by the GC after memory allocation and hence invalidated the C pointer. This patch removes the indirection of C pointer and uses OCaml macro to access values directly.
Only Mmap.read function had this problem. The other functions, despite having the same code style, didn't have memory allocation involved hence wouldn't intrigue such an error. I've changed all of them to the safer style for future proof. Directly casting OCaml value's *data block* (rather than the value itself) as a C pointer is not a common practice either, but I'll leave it as it is.
The bug hadn't occured on XenServer because XenServer didn't make use of the Mmap.read function (except in one place for debugging). In XenServer, most mmap operations were going through another pair of separately implemented functions (Xs_ring.read/write).
Signed-off-by: Zheng Li <dev@zheng.li>
diff --git a/tools/ocaml/libs/mmap/mmap_stubs.c b/tools/ocaml/libs/mmap/mmap_stubs.c
--- a/tools/ocaml/libs/mmap/mmap_stubs.c
+++ b/tools/ocaml/libs/mmap/mmap_stubs.c
@@ -71,12 +71,10 @@ CAMLprim value stub_mmap_init(value fd,
CAMLprim value stub_mmap_final(value interface)
{
CAMLparam1(interface);
- struct mmap_interface *intf;
- intf = GET_C_STRUCT(interface);
- if (intf->addr != MAP_FAILED)
- munmap(intf->addr, intf->len);
- intf->addr = MAP_FAILED;
+ if (GET_C_STRUCT(interface)->addr != MAP_FAILED)
+ munmap(GET_C_STRUCT(interface)->addr, GET_C_STRUCT(interface)->len);
+ GET_C_STRUCT(interface)->addr = MAP_FAILED;
CAMLreturn(Val_unit);
}
@@ -85,21 +83,19 @@ CAMLprim value stub_mmap_read(value inte
{
CAMLparam3(interface, start, len);
CAMLlocal1(data);
- struct mmap_interface *intf;
int c_start;
int c_len;
c_start = Int_val(start);
c_len = Int_val(len);
- intf = GET_C_STRUCT(interface);
- if (c_start > intf->len)
+ if (c_start > GET_C_STRUCT(interface)->len)
caml_invalid_argument("start invalid");
- if (c_start + c_len > intf->len)
+ if (c_start + c_len > GET_C_STRUCT(interface)->len)
caml_invalid_argument("len invalid");
data = caml_alloc_string(c_len);
- memcpy((char *) data, intf->addr + c_start, c_len);
+ memcpy((char *) data, GET_C_STRUCT(interface)->addr + c_start, c_len);
CAMLreturn(data);
}
@@ -108,20 +104,18 @@ CAMLprim value stub_mmap_write(value int
value start, value len)
{
CAMLparam4(interface, data, start, len);
- struct mmap_interface *intf;
int c_start;
int c_len;
c_start = Int_val(start);
c_len = Int_val(len);
- intf = GET_C_STRUCT(interface);
- if (c_start > intf->len)
+ if (c_start > GET_C_STRUCT(interface)->len)
caml_invalid_argument("start invalid");
- if (c_start + c_len > intf->len)
+ if (c_start + c_len > GET_C_STRUCT(interface)->len)
caml_invalid_argument("len invalid");
- memcpy(intf->addr + c_start, (char *) data, c_len);
+ memcpy(GET_C_STRUCT(interface)->addr + c_start, (char *) data, c_len);
CAMLreturn(Val_unit);
}
[-- Attachment #3: Type: text/plain, Size: 138 bytes --]
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^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH 2 of 2] Change GET_C_STRUCT to Intf_val to follow the common naming scheme of OCaml macro
2011-09-30 15:39 [PATCH 0 of 2] Invalid memory access in OCaml mmap library Zheng Li
2011-09-30 15:39 ` [PATCH 1 of 2] Fix invalid memory access in OCaml mmap library (to play nicely with the GC) Zheng Li
@ 2011-09-30 15:40 ` Zheng Li
1 sibling, 0 replies; 6+ messages in thread
From: Zheng Li @ 2011-09-30 15:40 UTC (permalink / raw)
To: xen-devel
[-- Attachment #1: Type: text/plain, Size: 3181 bytes --]
... and for better readabilities.
Signed-off-by: Zheng Li <dev@zheng.li>
tools/ocaml/libs/mmap/mmap_stubs.c | 34 +++++++++++++++++-----------------
1 files changed, 17 insertions(+), 17 deletions(-)
----
diff --git a/tools/ocaml/libs/mmap/mmap_stubs.c b/tools/ocaml/libs/mmap/mmap_stubs.c
--- a/tools/ocaml/libs/mmap/mmap_stubs.c
+++ b/tools/ocaml/libs/mmap/mmap_stubs.c
@@ -28,7 +28,7 @@
#include <caml/fail.h>
#include <caml/callback.h>
-#define GET_C_STRUCT(a) ((struct mmap_interface *) a)
+#define Intf_val(a) ((struct mmap_interface *) a)
static int mmap_interface_init(struct mmap_interface *intf,
int fd, int pflag, int mflag,
@@ -61,27 +61,27 @@ CAMLprim value stub_mmap_init(value fd,
result = caml_alloc(sizeof(struct mmap_interface), Abstract_tag);
- if (mmap_interface_init(GET_C_STRUCT(result), Int_val(fd),
+ if (mmap_interface_init(Intf_val(result), Int_val(fd),
c_pflag, c_mflag,
Int_val(len), Int_val(offset)))
caml_failwith("mmap");
CAMLreturn(result);
}
-CAMLprim value stub_mmap_final(value interface)
+CAMLprim value stub_mmap_final(value intf)
{
- CAMLparam1(interface);
+ CAMLparam1(intf);
- if (GET_C_STRUCT(interface)->addr != MAP_FAILED)
- munmap(GET_C_STRUCT(interface)->addr, GET_C_STRUCT(interface)->len);
- GET_C_STRUCT(interface)->addr = MAP_FAILED;
+ if (Intf_val(intf)->addr != MAP_FAILED)
+ munmap(Intf_val(intf)->addr, Intf_val(intf)->len);
+ Intf_val(intf)->addr = MAP_FAILED;
CAMLreturn(Val_unit);
}
-CAMLprim value stub_mmap_read(value interface, value start, value len)
+CAMLprim value stub_mmap_read(value intf, value start, value len)
{
- CAMLparam3(interface, start, len);
+ CAMLparam3(intf, start, len);
CAMLlocal1(data);
int c_start;
int c_len;
@@ -89,33 +89,33 @@ CAMLprim value stub_mmap_read(value inte
c_start = Int_val(start);
c_len = Int_val(len);
- if (c_start > GET_C_STRUCT(interface)->len)
+ if (c_start > Intf_val(intf)->len)
caml_invalid_argument("start invalid");
- if (c_start + c_len > GET_C_STRUCT(interface)->len)
+ if (c_start + c_len > Intf_val(intf)->len)
caml_invalid_argument("len invalid");
data = caml_alloc_string(c_len);
- memcpy((char *) data, GET_C_STRUCT(interface)->addr + c_start, c_len);
+ memcpy((char *) data, Intf_val(intf)->addr + c_start, c_len);
CAMLreturn(data);
}
-CAMLprim value stub_mmap_write(value interface, value data,
+CAMLprim value stub_mmap_write(value intf, value data,
value start, value len)
{
- CAMLparam4(interface, data, start, len);
+ CAMLparam4(intf, data, start, len);
int c_start;
int c_len;
c_start = Int_val(start);
c_len = Int_val(len);
- if (c_start > GET_C_STRUCT(interface)->len)
+ if (c_start > Intf_val(intf)->len)
caml_invalid_argument("start invalid");
- if (c_start + c_len > GET_C_STRUCT(interface)->len)
+ if (c_start + c_len > Intf_val(intf)->len)
caml_invalid_argument("len invalid");
- memcpy(GET_C_STRUCT(interface)->addr + c_start, (char *) data, c_len);
+ memcpy(Intf_val(intf)->addr + c_start, (char *) data, c_len);
CAMLreturn(Val_unit);
}
[-- Attachment #2: xen-unstable.hg-2.patch --]
[-- Type: text/x-patch, Size: 3044 bytes --]
... and for better readabilities.
Signed-off-by: Zheng Li <dev@zheng.li>
diff --git a/tools/ocaml/libs/mmap/mmap_stubs.c b/tools/ocaml/libs/mmap/mmap_stubs.c
--- a/tools/ocaml/libs/mmap/mmap_stubs.c
+++ b/tools/ocaml/libs/mmap/mmap_stubs.c
@@ -28,7 +28,7 @@
#include <caml/fail.h>
#include <caml/callback.h>
-#define GET_C_STRUCT(a) ((struct mmap_interface *) a)
+#define Intf_val(a) ((struct mmap_interface *) a)
static int mmap_interface_init(struct mmap_interface *intf,
int fd, int pflag, int mflag,
@@ -61,27 +61,27 @@ CAMLprim value stub_mmap_init(value fd,
result = caml_alloc(sizeof(struct mmap_interface), Abstract_tag);
- if (mmap_interface_init(GET_C_STRUCT(result), Int_val(fd),
+ if (mmap_interface_init(Intf_val(result), Int_val(fd),
c_pflag, c_mflag,
Int_val(len), Int_val(offset)))
caml_failwith("mmap");
CAMLreturn(result);
}
-CAMLprim value stub_mmap_final(value interface)
+CAMLprim value stub_mmap_final(value intf)
{
- CAMLparam1(interface);
+ CAMLparam1(intf);
- if (GET_C_STRUCT(interface)->addr != MAP_FAILED)
- munmap(GET_C_STRUCT(interface)->addr, GET_C_STRUCT(interface)->len);
- GET_C_STRUCT(interface)->addr = MAP_FAILED;
+ if (Intf_val(intf)->addr != MAP_FAILED)
+ munmap(Intf_val(intf)->addr, Intf_val(intf)->len);
+ Intf_val(intf)->addr = MAP_FAILED;
CAMLreturn(Val_unit);
}
-CAMLprim value stub_mmap_read(value interface, value start, value len)
+CAMLprim value stub_mmap_read(value intf, value start, value len)
{
- CAMLparam3(interface, start, len);
+ CAMLparam3(intf, start, len);
CAMLlocal1(data);
int c_start;
int c_len;
@@ -89,33 +89,33 @@ CAMLprim value stub_mmap_read(value inte
c_start = Int_val(start);
c_len = Int_val(len);
- if (c_start > GET_C_STRUCT(interface)->len)
+ if (c_start > Intf_val(intf)->len)
caml_invalid_argument("start invalid");
- if (c_start + c_len > GET_C_STRUCT(interface)->len)
+ if (c_start + c_len > Intf_val(intf)->len)
caml_invalid_argument("len invalid");
data = caml_alloc_string(c_len);
- memcpy((char *) data, GET_C_STRUCT(interface)->addr + c_start, c_len);
+ memcpy((char *) data, Intf_val(intf)->addr + c_start, c_len);
CAMLreturn(data);
}
-CAMLprim value stub_mmap_write(value interface, value data,
+CAMLprim value stub_mmap_write(value intf, value data,
value start, value len)
{
- CAMLparam4(interface, data, start, len);
+ CAMLparam4(intf, data, start, len);
int c_start;
int c_len;
c_start = Int_val(start);
c_len = Int_val(len);
- if (c_start > GET_C_STRUCT(interface)->len)
+ if (c_start > Intf_val(intf)->len)
caml_invalid_argument("start invalid");
- if (c_start + c_len > GET_C_STRUCT(interface)->len)
+ if (c_start + c_len > Intf_val(intf)->len)
caml_invalid_argument("len invalid");
- memcpy(GET_C_STRUCT(interface)->addr + c_start, (char *) data, c_len);
+ memcpy(Intf_val(intf)->addr + c_start, (char *) data, c_len);
CAMLreturn(Val_unit);
}
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