On Sat, May 6, 2023 at 11:36 AM Finn Thain <fthain@xxxxxxxxxxxxxx> wrote: > On 68030/020, an instruction such as, moveml %a2-%a3/%a5,%sp@- may cause > a stack page fault during instruction execution (i.e. not at an > instruction boundary) and produce a format 0xB exception frame. > > In this situation, the value of USP will be unreliable. If a signal is to > be delivered following the exception, this USP value is used to calculate > the location for a signal frame. This can result in a corrupted user > stack. > > The corruption was detected in dash (actually in glibc) where it showed > up as an intermittent "stack smashing detected" message and crash > following signal delivery for SIGCHLD. > > It was hard to reproduce that failure because delivery of the signal > raced with the page fault and because the kernel places an unpredictable > gap of up to 7 bytes between the USP and the signal frame. > > A format 0xB exception frame can be produced by a bus error or an address > error. The 68030 Users Manual says that address errors occur immediately > upon detection during instruction prefetch. The instruction pipeline > allows prefetch to overlap with other instructions, which means an > address error can arise during the execution of a different instruction. > So it seems likely that this patch may help in the address error case also. > > Reported-and-tested-by: Stan Johnson <userm57@xxxxxxxxx> > Link: https://lore.kernel.org/all/CAMuHMdW3yD22_ApemzW_6me3adq6A458u1_F0v-1EYwK_62jPA@xxxxxxxxxxxxxx/ > Cc: Michael Schmitz <schmitzmic@xxxxxxxxx> > Cc: Andreas Schwab <schwab@xxxxxxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > Co-developed-by: Michael Schmitz <schmitzmic@xxxxxxxxx> > Signed-off-by: Michael Schmitz <schmitzmic@xxxxxxxxx> > Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxx> Reviewed-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> i.e. will queue as a fix in the m68k for-v6.4 branch. I plan to send this upstream later this week, so any additional testing would be appreciated. Thanks! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
