ALSA: add new 32-bit layout for snd_pcm_mmap_status/control

The snd_pcm_mmap_status and snd_pcm_mmap_control interfaces are one of the
trickiest areas to get right when moving to 64-bit time_t in user space.

The snd_pcm_mmap_status structure layout is incompatible with user space
that uses a 64-bit time_t, so we need a new layout for it. Since the
SNDRV_PCM_IOCTL_SYNC_PTR ioctl combines it with snd_pcm_mmap_control
into snd_pcm_sync_ptr, we need to change those two as well.

Both structures are also exported via an mmap() operation on certain
architectures, and this suffers from incompatibility between 32-bit
and 64-bit user space. As we have to change both structures anyway,
this is a good opportunity to fix the mmap() problem as well, so let's
standardize on the existing 64-bit layout of the structure where possible.

The downside is that we lose mmap() support for existing 32-bit x86 and
powerpc applications, adding that would introduce very noticeable runtime
overhead and complexity. My assumption here is that not too many people
will miss the removed feature, given that:

- Almost all x86 and powerpc users these days are on 64-bit kernels,
the majority of today's 32-bit users are on architectures that never
supported mmap (ARM, MIPS, ...).
- It never worked in compat mode (it was intentionally disabled there)
- The application already needs to work with a fallback to
SNDRV_PCM_IOCTL_SYNC_PTR, which will keep working with both the old
and new structure layout.

Both the ioctl() and mmap() based interfaces are changed at the same
time, as they are based on the same structures. Unlike other interfaces,
we change the uapi header to export both the traditional structure and
a version that is portable between 32-bit and 64-bit user space code
and that corresponds to the existing 64-bit layout. We further check the
__USE_TIME_BITS64 macro that will be defined by future C library versions
whenever we use the new time_t definition, so any existing user space
source code will not see any changes until it gets rebuilt against a new
C library. However, the new structures are all visible in addition to the
old ones, allowing applications to explicitly request the new structures.

In order to detect the difference between the old snd_pcm_mmap_status and
the new __snd_pcm_mmap_status64 structure from the ioctl command number,
we rely on one quirk in the structure definition: snd_pcm_mmap_status
must be aligned to alignof(time_t), which leads the compiler to insert
four bytes of padding in struct snd_pcm_sync_ptr after 'flags' and a
corresponding change in the size of snd_pcm_sync_ptr itself. On x86-32
(and only there), the compiler doesn't use 64-bit alignment in structure,
so I'm adding an explicit pad in the structure that has no effect on the
existing 64-bit architectures but ensures that the layout matches for x86.

The snd_pcm_uframes_t type compatibility requires another hack: we can't
easily make that 64 bit wide, so I leave the type as 'unsigned long',
but add padding before and after it, to ensure that the data is properly
aligned to the respective 64-bit field in the in-kernel structure.

For the SNDRV_PCM_MMAP_OFFSET_STATUS/CONTROL constants that are used
as the virtual file offset in the mmap() function, we also have to
introduce new constants that depend on hte __USE_TIME_BITS64 macro:
The existing macros are renamed to SNDRV_PCM_MMAP_OFFSET_STATUS_OLD
and SNDRV_PCM_MMAP_OFFSET_CONTROL_OLD, they continue to work fine on
64-bit architectures, but stop working on native 32-bit user space.
The replacement _NEW constants are now used by default for user space
built with __USE_TIME_BITS64, those now work on all new kernels for x86,
ppc and alpha (32 and 64 bit, native and compat). It might be a good idea
for a future alsa-lib to support both the _OLD and _NEW macros and use
the corresponding structures directly. Unmodified alsa-lib source code
will retain the current behavior, so it will no longer be able to use
mmap() for the status/control structures on 32-bit systems, until either
the C library gets updated to 64-bit time_t or alsa-lib gets updated to
support both mmap() layouts.

Co-developed-with: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 17 insertions, 13 deletions

diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
index 6a2e5ea145e6..967c689fb8da 100644
--- a/sound/core/pcm_compat.c
+++ b/sound/core/pcm_compat.c
@@ -178,8 +178,6 @@ struct compat_snd_pcm_status64 {
 	unsigned char reserved[52-4*sizeof(s64)];
 } __packed;
 
-#define put_timespec(src, dst) copy_to_user(dst, src, sizeof(*dst))
-
 static int snd_pcm_status_user_compat64(struct snd_pcm_substream *substream,
 					struct compat_snd_pcm_status64 __user *src,
 					bool ext)
@@ -382,10 +380,12 @@ struct snd_pcm_mmap_status_x32 {
 	s32 pad1;
 	u32 hw_ptr;
 	u32 pad2; /* alignment */
-	struct timespec tstamp;
+	s64 tstamp_sec;
+	s64 tstamp_nsec;
 	s32 suspended_state;
 	s32 pad3;
-	struct timespec audio_tstamp;
+	s64 audio_tstamp_sec;
+	s64 audio_tstamp_nsec;
 } __packed;
 
 struct snd_pcm_mmap_control_x32 {
@@ -453,9 +453,11 @@ static int snd_pcm_ioctl_sync_ptr_x32(struct snd_pcm_substream *substream,
 	snd_pcm_stream_unlock_irq(substream);
 	if (put_user(sstatus.state, &src->s.status.state) ||
 	    put_user(sstatus.hw_ptr, &src->s.status.hw_ptr) ||
-	    put_timespec(&sstatus.tstamp, &src->s.status.tstamp) ||
+	    put_user(sstatus.tstamp.tv_sec, &src->s.status.tstamp_sec) ||
+	    put_user(sstatus.tstamp.tv_nsec, &src->s.status.tstamp_nsec) ||
 	    put_user(sstatus.suspended_state, &src->s.status.suspended_state) ||
-	    put_timespec(&sstatus.audio_tstamp, &src->s.status.audio_tstamp) ||
+	    put_user(sstatus.audio_tstamp.tv_sec, &src->s.status.audio_tstamp_sec) ||
+	    put_user(sstatus.audio_tstamp.tv_nsec, &src->s.status.audio_tstamp_nsec) ||
 	    put_user(scontrol.appl_ptr, &src->c.control.appl_ptr) ||
 	    put_user(scontrol.avail_min, &src->c.control.avail_min))
 		return -EFAULT;
@@ -480,7 +482,6 @@ enum {
 	SNDRV_PCM_IOCTL_READI_FRAMES32 = _IOR('A', 0x51, struct snd_xferi32),
 	SNDRV_PCM_IOCTL_WRITEN_FRAMES32 = _IOW('A', 0x52, struct snd_xfern32),
 	SNDRV_PCM_IOCTL_READN_FRAMES32 = _IOR('A', 0x53, struct snd_xfern32),
-	SNDRV_PCM_IOCTL_SYNC_PTR32 = _IOWR('A', 0x23, struct snd_pcm_sync_ptr32),
 	SNDRV_PCM_IOCTL_STATUS_COMPAT64 = _IOR('A', 0x20, struct compat_snd_pcm_status64),
 	SNDRV_PCM_IOCTL_STATUS_EXT_COMPAT64 = _IOWR('A', 0x24, struct compat_snd_pcm_status64),
 #ifdef CONFIG_X86_X32
@@ -504,8 +505,8 @@ static long snd_pcm_ioctl_compat(struct file *file, unsigned int cmd, unsigned l
 
 	/*
 	 * When PCM is used on 32bit mode, we need to disable
-	 * mmap of PCM status/control records because of the size
-	 * incompatibility.
+	 * mmap of the old PCM status/control records because
+	 * of the size incompatibility.
 	 */
 	pcm_file->no_compat_mmap = 1;
 
@@ -527,6 +528,13 @@ static long snd_pcm_ioctl_compat(struct file *file, unsigned int cmd, unsigned l
 	case SNDRV_PCM_IOCTL_XRUN:
 	case SNDRV_PCM_IOCTL_LINK:
 	case SNDRV_PCM_IOCTL_UNLINK:
+	case __SNDRV_PCM_IOCTL_SYNC_PTR32:
+		return snd_pcm_common_ioctl(file, substream, cmd, argp);
+	case __SNDRV_PCM_IOCTL_SYNC_PTR64:
+#ifdef CONFIG_X86_X32
+		if (in_x32_syscall())
+			return snd_pcm_ioctl_sync_ptr_x32(substream, argp);
+#endif /* CONFIG_X86_X32 */
 		return snd_pcm_common_ioctl(file, substream, cmd, argp);
 	case SNDRV_PCM_IOCTL_HW_REFINE32:
 		return snd_pcm_ioctl_hw_params_compat(substream, 1, argp);
@@ -538,8 +546,6 @@ static long snd_pcm_ioctl_compat(struct file *file, unsigned int cmd, unsigned l
 		return snd_pcm_status_user32(substream, argp, false);
 	case SNDRV_PCM_IOCTL_STATUS_EXT_COMPAT32:
 		return snd_pcm_status_user32(substream, argp, true);
-	case SNDRV_PCM_IOCTL_SYNC_PTR32:
-		return snd_pcm_ioctl_sync_ptr_compat(substream, argp);
 	case SNDRV_PCM_IOCTL_CHANNEL_INFO32:
 		return snd_pcm_ioctl_channel_info_compat(substream, argp);
 	case SNDRV_PCM_IOCTL_WRITEI_FRAMES32:
@@ -561,8 +567,6 @@ static long snd_pcm_ioctl_compat(struct file *file, unsigned int cmd, unsigned l
 	case SNDRV_PCM_IOCTL_STATUS_EXT_COMPAT64:
 		return snd_pcm_status_user_compat64(substream, argp, true);
 #ifdef CONFIG_X86_X32
-	case SNDRV_PCM_IOCTL_SYNC_PTR_X32:
-		return snd_pcm_ioctl_sync_ptr_x32(substream, argp);
 	case SNDRV_PCM_IOCTL_CHANNEL_INFO_X32:
 		return snd_pcm_ioctl_channel_info_x32(substream, argp);
 #endif /* CONFIG_X86_X32 */