linux-user: add memfd_create
diff mbox series

Message ID 20190816211049.57317-1-scw@google.com
State New
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  • linux-user: add memfd_create
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Commit Message

Sam Eiderman via Aug. 16, 2019, 9:10 p.m. UTC
Add support for the memfd_create syscall. If the host does not have the
libc wrapper, translate to a direct syscall with NC-macro.

Buglink: https://bugs.launchpad.net/qemu/+bug/1734792
Signed-off-by: Shu-Chun Weng <scw@google.com>
---
 include/qemu/memfd.h |  4 ++++
 linux-user/syscall.c | 11 +++++++++++
 util/memfd.c         |  2 +-
 3 files changed, 16 insertions(+), 1 deletion(-)

Comments

Philippe Mathieu-Daudé Aug. 18, 2019, 9:57 p.m. UTC | #1
Cc'ing Marc-André

On 8/16/19 11:10 PM, Shu-Chun Weng via Qemu-devel wrote:
> Add support for the memfd_create syscall. If the host does not have the
> libc wrapper, translate to a direct syscall with NC-macro.
> 
> Buglink: https://bugs.launchpad.net/qemu/+bug/1734792
> Signed-off-by: Shu-Chun Weng <scw@google.com>
> ---
>  include/qemu/memfd.h |  4 ++++
>  linux-user/syscall.c | 11 +++++++++++
>  util/memfd.c         |  2 +-
>  3 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
> index d551c28b68..975b6bdb77 100644
> --- a/include/qemu/memfd.h
> +++ b/include/qemu/memfd.h
> @@ -32,6 +32,10 @@
>  #define MFD_HUGE_SHIFT 26
>  #endif
>  
> +#if defined CONFIG_LINUX && !defined CONFIG_MEMFD
> +int memfd_create(const char *name, unsigned int flags);
> +#endif
> +
>  int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
>                        uint64_t hugetlbsize, unsigned int seals, Error **errp);
>  bool qemu_memfd_alloc_check(void);
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 8367cb138d..b506c1f40e 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -20,6 +20,7 @@
>  #include "qemu/osdep.h"
>  #include "qemu/cutils.h"
>  #include "qemu/path.h"
> +#include "qemu/memfd.h"
>  #include <elf.h>
>  #include <endian.h>
>  #include <grp.h>
> @@ -11938,6 +11939,16 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
>          /* PowerPC specific.  */
>          return do_swapcontext(cpu_env, arg1, arg2, arg3);
>  #endif
> +#ifdef TARGET_NR_memfd_create
> +    case TARGET_NR_memfd_create:
> +        p = lock_user_string(arg1);
> +        if (!p) {
> +            return -TARGET_EFAULT;
> +        }
> +        ret = get_errno(memfd_create(p, arg2));
> +        unlock_user(p, arg1, 0);
> +        return ret;
> +#endif
>  
>      default:
>          qemu_log_mask(LOG_UNIMP, "Unsupported syscall: %d\n", num);
> diff --git a/util/memfd.c b/util/memfd.c
> index 00334e5b21..4a3c07e0be 100644
> --- a/util/memfd.c
> +++ b/util/memfd.c
> @@ -35,7 +35,7 @@
>  #include <sys/syscall.h>
>  #include <asm/unistd.h>
>  
> -static int memfd_create(const char *name, unsigned int flags)
> +int memfd_create(const char *name, unsigned int flags)
>  {
>  #ifdef __NR_memfd_create
>      return syscall(__NR_memfd_create, name, flags);
>
Marc-André Lureau Aug. 19, 2019, 7:12 a.m. UTC | #2
On Sat, Aug 17, 2019 at 1:28 AM Shu-Chun Weng via Qemu-devel
<qemu-devel@nongnu.org> wrote:
>
> Add support for the memfd_create syscall. If the host does not have the
> libc wrapper, translate to a direct syscall with NC-macro.
>
> Buglink: https://bugs.launchpad.net/qemu/+bug/1734792
> Signed-off-by: Shu-Chun Weng <scw@google.com>

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

> ---
>  include/qemu/memfd.h |  4 ++++
>  linux-user/syscall.c | 11 +++++++++++
>  util/memfd.c         |  2 +-
>  3 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
> index d551c28b68..975b6bdb77 100644
> --- a/include/qemu/memfd.h
> +++ b/include/qemu/memfd.h
> @@ -32,6 +32,10 @@
>  #define MFD_HUGE_SHIFT 26
>  #endif
>
> +#if defined CONFIG_LINUX && !defined CONFIG_MEMFD
> +int memfd_create(const char *name, unsigned int flags);
> +#endif
> +
>  int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
>                        uint64_t hugetlbsize, unsigned int seals, Error **errp);
>  bool qemu_memfd_alloc_check(void);
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 8367cb138d..b506c1f40e 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -20,6 +20,7 @@
>  #include "qemu/osdep.h"
>  #include "qemu/cutils.h"
>  #include "qemu/path.h"
> +#include "qemu/memfd.h"
>  #include <elf.h>
>  #include <endian.h>
>  #include <grp.h>
> @@ -11938,6 +11939,16 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
>          /* PowerPC specific.  */
>          return do_swapcontext(cpu_env, arg1, arg2, arg3);
>  #endif
> +#ifdef TARGET_NR_memfd_create
> +    case TARGET_NR_memfd_create:
> +        p = lock_user_string(arg1);
> +        if (!p) {
> +            return -TARGET_EFAULT;
> +        }
> +        ret = get_errno(memfd_create(p, arg2));
> +        unlock_user(p, arg1, 0);
> +        return ret;
> +#endif
>
>      default:
>          qemu_log_mask(LOG_UNIMP, "Unsupported syscall: %d\n", num);
> diff --git a/util/memfd.c b/util/memfd.c
> index 00334e5b21..4a3c07e0be 100644
> --- a/util/memfd.c
> +++ b/util/memfd.c
> @@ -35,7 +35,7 @@
>  #include <sys/syscall.h>
>  #include <asm/unistd.h>
>
> -static int memfd_create(const char *name, unsigned int flags)
> +int memfd_create(const char *name, unsigned int flags)
>  {
>  #ifdef __NR_memfd_create
>      return syscall(__NR_memfd_create, name, flags);
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>
>
Peter Maydell Aug. 19, 2019, 11:56 a.m. UTC | #3
On Fri, 16 Aug 2019 at 22:28, Shu-Chun Weng via Qemu-devel
<qemu-devel@nongnu.org> wrote:
>
> Add support for the memfd_create syscall. If the host does not have the
> libc wrapper, translate to a direct syscall with NC-macro.
>
> Buglink: https://bugs.launchpad.net/qemu/+bug/1734792
> Signed-off-by: Shu-Chun Weng <scw@google.com>
> ---
>  include/qemu/memfd.h |  4 ++++
>  linux-user/syscall.c | 11 +++++++++++
>  util/memfd.c         |  2 +-
>  3 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
> index d551c28b68..975b6bdb77 100644
> --- a/include/qemu/memfd.h
> +++ b/include/qemu/memfd.h
> @@ -32,6 +32,10 @@
>  #define MFD_HUGE_SHIFT 26
>  #endif
>
> +#if defined CONFIG_LINUX && !defined CONFIG_MEMFD
> +int memfd_create(const char *name, unsigned int flags);
> +#endif
> +
>  int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
>                        uint64_t hugetlbsize, unsigned int seals, Error **errp);
>  bool qemu_memfd_alloc_check(void);
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 8367cb138d..b506c1f40e 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -20,6 +20,7 @@
>  #include "qemu/osdep.h"
>  #include "qemu/cutils.h"
>  #include "qemu/path.h"
> +#include "qemu/memfd.h"
>  #include <elf.h>
>  #include <endian.h>
>  #include <grp.h>
> @@ -11938,6 +11939,16 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
>          /* PowerPC specific.  */
>          return do_swapcontext(cpu_env, arg1, arg2, arg3);
>  #endif
> +#ifdef TARGET_NR_memfd_create
> +    case TARGET_NR_memfd_create:
> +        p = lock_user_string(arg1);
> +        if (!p) {
> +            return -TARGET_EFAULT;
> +        }
> +        ret = get_errno(memfd_create(p, arg2));

I think here you may need to call
           fd_trans_unregister(ret);

since memfd_create() returns a file descriptor.
(This call unregisters any pre-existing hooks for "we need
to mangle the data for reads/writes of this file descriptor",
in case the fd was previously being used for a file descriptor
type that needed that.) This is what eg NR_open does.

Laurent -- do I have this right? It's not entirely clear
to me that we could ever be in a situation where a syscall
like open or memfd_create returns an fd that's got an fd_trans
hook active, because that would imply we'd failed to delete
the hook on fd-close somehow. Is this just a belt-and-braces
bit of coding ?

thanks
-- PMM
Laurent Vivier Aug. 23, 2019, 4:42 p.m. UTC | #4
Le 19/08/2019 à 13:56, Peter Maydell a écrit :
> On Fri, 16 Aug 2019 at 22:28, Shu-Chun Weng via Qemu-devel
> <qemu-devel@nongnu.org> wrote:
>>
>> Add support for the memfd_create syscall. If the host does not have the
>> libc wrapper, translate to a direct syscall with NC-macro.
>>
>> Buglink: https://bugs.launchpad.net/qemu/+bug/1734792
>> Signed-off-by: Shu-Chun Weng <scw@google.com>
>> ---
>>  include/qemu/memfd.h |  4 ++++
>>  linux-user/syscall.c | 11 +++++++++++
>>  util/memfd.c         |  2 +-
>>  3 files changed, 16 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
>> index d551c28b68..975b6bdb77 100644
>> --- a/include/qemu/memfd.h
>> +++ b/include/qemu/memfd.h
>> @@ -32,6 +32,10 @@
>>  #define MFD_HUGE_SHIFT 26
>>  #endif
>>
>> +#if defined CONFIG_LINUX && !defined CONFIG_MEMFD
>> +int memfd_create(const char *name, unsigned int flags);
>> +#endif
>> +
>>  int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
>>                        uint64_t hugetlbsize, unsigned int seals, Error **errp);
>>  bool qemu_memfd_alloc_check(void);
>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>> index 8367cb138d..b506c1f40e 100644
>> --- a/linux-user/syscall.c
>> +++ b/linux-user/syscall.c
>> @@ -20,6 +20,7 @@
>>  #include "qemu/osdep.h"
>>  #include "qemu/cutils.h"
>>  #include "qemu/path.h"
>> +#include "qemu/memfd.h"
>>  #include <elf.h>
>>  #include <endian.h>
>>  #include <grp.h>
>> @@ -11938,6 +11939,16 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
>>          /* PowerPC specific.  */
>>          return do_swapcontext(cpu_env, arg1, arg2, arg3);
>>  #endif
>> +#ifdef TARGET_NR_memfd_create
>> +    case TARGET_NR_memfd_create:
>> +        p = lock_user_string(arg1);
>> +        if (!p) {
>> +            return -TARGET_EFAULT;
>> +        }
>> +        ret = get_errno(memfd_create(p, arg2));
> 
> I think here you may need to call
>            fd_trans_unregister(ret);
> 
> since memfd_create() returns a file descriptor.
> (This call unregisters any pre-existing hooks for "we need
> to mangle the data for reads/writes of this file descriptor",
> in case the fd was previously being used for a file descriptor
> type that needed that.) This is what eg NR_open does.
> 
> Laurent -- do I have this right? It's not entirely clear
> to me that we could ever be in a situation where a syscall
> like open or memfd_create returns an fd that's got an fd_trans
> hook active, because that would imply we'd failed to delete
> the hook on fd-close somehow. Is this just a belt-and-braces
> bit of coding ?

Exactly.

It's in case we missed one fd close and then to be sure an existing "fd
translator" will not mess with data of the new one.

Thanks,
Laurent
Laurent Vivier Sept. 10, 2019, 8:16 a.m. UTC | #5
Le 16/08/2019 à 23:10, Shu-Chun Weng via Qemu-devel a écrit :
> Add support for the memfd_create syscall. If the host does not have the
> libc wrapper, translate to a direct syscall with NC-macro.
> 
> Buglink: https://bugs.launchpad.net/qemu/+bug/1734792
> Signed-off-by: Shu-Chun Weng <scw@google.com>
> ---
>  include/qemu/memfd.h |  4 ++++
>  linux-user/syscall.c | 11 +++++++++++
>  util/memfd.c         |  2 +-
>  3 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
> index d551c28b68..975b6bdb77 100644
> --- a/include/qemu/memfd.h
> +++ b/include/qemu/memfd.h
> @@ -32,6 +32,10 @@
>  #define MFD_HUGE_SHIFT 26
>  #endif
>  
> +#if defined CONFIG_LINUX && !defined CONFIG_MEMFD
> +int memfd_create(const char *name, unsigned int flags);
> +#endif
> +
>  int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
>                        uint64_t hugetlbsize, unsigned int seals, Error **errp);
>  bool qemu_memfd_alloc_check(void);
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 8367cb138d..b506c1f40e 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -20,6 +20,7 @@
>  #include "qemu/osdep.h"
>  #include "qemu/cutils.h"
>  #include "qemu/path.h"
> +#include "qemu/memfd.h"
>  #include <elf.h>
>  #include <endian.h>
>  #include <grp.h>
> @@ -11938,6 +11939,16 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
>          /* PowerPC specific.  */
>          return do_swapcontext(cpu_env, arg1, arg2, arg3);
>  #endif
> +#ifdef TARGET_NR_memfd_create
> +    case TARGET_NR_memfd_create:
> +        p = lock_user_string(arg1);
> +        if (!p) {
> +            return -TARGET_EFAULT;
> +        }
> +        ret = get_errno(memfd_create(p, arg2));
> +        unlock_user(p, arg1, 0);
> +        return ret;
> +#endif
>  
>      default:
>          qemu_log_mask(LOG_UNIMP, "Unsupported syscall: %d\n", num);
> diff --git a/util/memfd.c b/util/memfd.c
> index 00334e5b21..4a3c07e0be 100644
> --- a/util/memfd.c
> +++ b/util/memfd.c
> @@ -35,7 +35,7 @@
>  #include <sys/syscall.h>
>  #include <asm/unistd.h>
>  
> -static int memfd_create(const char *name, unsigned int flags)
> +int memfd_create(const char *name, unsigned int flags)
>  {
>  #ifdef __NR_memfd_create
>      return syscall(__NR_memfd_create, name, flags);
> 

Applied to my linux-user branch.

Thanks,
Laurent

Patch
diff mbox series

diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
index d551c28b68..975b6bdb77 100644
--- a/include/qemu/memfd.h
+++ b/include/qemu/memfd.h
@@ -32,6 +32,10 @@ 
 #define MFD_HUGE_SHIFT 26
 #endif
 
+#if defined CONFIG_LINUX && !defined CONFIG_MEMFD
+int memfd_create(const char *name, unsigned int flags);
+#endif
+
 int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
                       uint64_t hugetlbsize, unsigned int seals, Error **errp);
 bool qemu_memfd_alloc_check(void);
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 8367cb138d..b506c1f40e 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -20,6 +20,7 @@ 
 #include "qemu/osdep.h"
 #include "qemu/cutils.h"
 #include "qemu/path.h"
+#include "qemu/memfd.h"
 #include <elf.h>
 #include <endian.h>
 #include <grp.h>
@@ -11938,6 +11939,16 @@  static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
         /* PowerPC specific.  */
         return do_swapcontext(cpu_env, arg1, arg2, arg3);
 #endif
+#ifdef TARGET_NR_memfd_create
+    case TARGET_NR_memfd_create:
+        p = lock_user_string(arg1);
+        if (!p) {
+            return -TARGET_EFAULT;
+        }
+        ret = get_errno(memfd_create(p, arg2));
+        unlock_user(p, arg1, 0);
+        return ret;
+#endif
 
     default:
         qemu_log_mask(LOG_UNIMP, "Unsupported syscall: %d\n", num);
diff --git a/util/memfd.c b/util/memfd.c
index 00334e5b21..4a3c07e0be 100644
--- a/util/memfd.c
+++ b/util/memfd.c
@@ -35,7 +35,7 @@ 
 #include <sys/syscall.h>
 #include <asm/unistd.h>
 
-static int memfd_create(const char *name, unsigned int flags)
+int memfd_create(const char *name, unsigned int flags)
 {
 #ifdef __NR_memfd_create
     return syscall(__NR_memfd_create, name, flags);