[v1,1/1] RTL8712 alignment bug in 3.6.5 on ARM

Commit Message

Larry Finger Nov. 18, 2012, 8:18 p.m. UTC

On 11/18/2012 12:11 PM, Andrew Lunn wrote:
>
> Just to clarify the issue here:
>
> union pn48 {
>          u64 val;
> #if defined(__BIG_ENDIAN)
>          struct {
>                  u8 TSC7;
>                  u8 TSC6;
>
> Any instance of pn48 needs to be 64 bit aligned when the val member of
> the union is used. The structure sta_info contains two such pn48s, so
> the code allocating the pool of these needs to ensure it allocated
> them 64 bit aligned, not 32bit aligned as it currently is.

Andrew,

For my education, would the following patch ensure 64-bit alignment for the pn48 
instances, or is more needed?


Thanks,

Larry

Comments

Andrew Lunn Nov. 18, 2012, 8:55 p.m. UTC | #1

On Sun, Nov 18, 2012 at 02:18:37PM -0600, Larry Finger wrote:
> On 11/18/2012 12:11 PM, Andrew Lunn wrote:
> >
> >Just to clarify the issue here:
> >
> >union pn48 {
> >         u64 val;
> >#if defined(__BIG_ENDIAN)
> >         struct {
> >                 u8 TSC7;
> >                 u8 TSC6;
> >
> >Any instance of pn48 needs to be 64 bit aligned when the val member of
> >the union is used. The structure sta_info contains two such pn48s, so
> >the code allocating the pool of these needs to ensure it allocated
> >them 64 bit aligned, not 32bit aligned as it currently is.
> 
> Andrew,
> 
> For my education, would the following patch ensure 64-bit alignment
> for the pn48 instances, or is more needed?

This is not sufficient. In fact it makes no difference at all. The
problem is not with the structure, but with the allocation of memory
used to contain the structure.

        pstapriv->pallocated_stainfo_buf = _malloc(sizeof(struct sta_info) *
                                                   NUM_STA + 4);
        if (pstapriv->pallocated_stainfo_buf == NULL)
                return _FAIL;
        pstapriv->pstainfo_buf = pstapriv->pallocated_stainfo_buf + 4 -
                ((addr_t)(pstapriv->pallocated_stainfo_buf) & 3);

kmalloc() guarantees that its alignment is correct for any type of
structure. Thus all this code above is redundant in Linux, but maybe
needed in some other OS. Worse still, this code actually breaks the
alignment. kmalloc() gave out something which was 64 bit aligned. But
by adding 4 and then masking off the lower 2 bits, it destroys the 64
bit alignment and makes it only 32bit aligned.

Removing the _malloc() wrapper, fixing the GFP_ATOMIC, and leaving the
allocater to worry about alignment will be one of the steps to getting
out of staging.

    Andrew

Larry Finger Nov. 19, 2012, 12:10 a.m. UTC | #2

On 11/18/2012 02:55 PM, Andrew Lunn wrote:

> This is not sufficient. In fact it makes no difference at all. The
> problem is not with the structure, but with the allocation of memory
> used to contain the structure.
>
>          pstapriv->pallocated_stainfo_buf = _malloc(sizeof(struct sta_info) *
>                                                     NUM_STA + 4);
>          if (pstapriv->pallocated_stainfo_buf == NULL)
>                  return _FAIL;
>          pstapriv->pstainfo_buf = pstapriv->pallocated_stainfo_buf + 4 -
>                  ((addr_t)(pstapriv->pallocated_stainfo_buf) & 3);
>
> kmalloc() guarantees that its alignment is correct for any type of
> structure. Thus all this code above is redundant in Linux, but maybe
> needed in some other OS. Worse still, this code actually breaks the
> alignment. kmalloc() gave out something which was 64 bit aligned. But
> by adding 4 and then masking off the lower 2 bits, it destroys the 64
> bit alignment and makes it only 32bit aligned.
>
> Removing the _malloc() wrapper, fixing the GFP_ATOMIC, and leaving the
> allocater to worry about alignment will be one of the steps to getting
> out of staging.

As you surmised, the original driver was meant for several Windows systems as 
well as Linux.

This driver will not make it out of staging until it supports the mac80211 
stack. Work to accomplish this has started by modifying the rtl8192se code to 
work with the USB interface. I will make certain that the alignment issues are 
fixed there.

Thanks for the lesson,

Larry

Patch

Index: staging/drivers/staging/rtl8712/rtl871x_security.h
===================================================================
--- staging.orig/drivers/staging/rtl8712/rtl871x_security.h
+++ staging/drivers/staging/rtl8712/rtl871x_security.h
@@ -89,6 +89,8 @@  struct RT_PMKID_LIST {
  };

  struct security_priv {
+       union pn48 Grptxpn;             /* PN48 used for Grp Key xmit. */
+       union pn48 Grprxpn;             /* PN48 used for Grp Key recv. */
         u32 AuthAlgrthm;                /* 802.11 auth, could be open, shared,
                                          * 8021x and authswitch */
         u32 PrivacyAlgrthm;             /* This specify the privacy for shared
@@ -104,8 +106,6 @@  struct security_priv {
                                          * inx0 and inx1 */
         union Keytype   XGrptxmickey[2];
         union Keytype   XGrprxmickey[2];
-       union pn48 Grptxpn;             /* PN48 used for Grp Key xmit. */
-       union pn48 Grprxpn;             /* PN48 used for Grp Key recv. */
         u8 wps_hw_pbc_pressed;/*for hw pbc pressed*/
         u8 wps_phase;/*for wps*/
         u8 wps_ie[MAX_WPA_IE_LEN<<2];