* Re: 2.6.9-rc2-mm2: devmem_is_allowed
2004-09-24 6:40 ` Arjan van de Ven
@ 2004-09-24 8:09 ` Martin Diehl
2004-09-24 8:11 ` Arjan van de Ven
0 siblings, 1 reply; 4+ messages in thread
From: Martin Diehl @ 2004-09-24 8:09 UTC (permalink / raw)
To: Arjan van de Ven; +Cc: Andrew Morton, linux-kernel
On Fri, 24 Sep 2004, Arjan van de Ven wrote:
> On Fri, 2004-09-24 at 00:37, Martin Diehl wrote:
> > Hi,
> >
> > after switching from working 2.6.9-rc2 to -mm2, X refused to start on my
> > testbox. It turned out this was because it failed (EPERM) reading from
> > /dev/mem beyond the 1MB limit.
>
> can you get me a strace of the failing X server?
> The code as is is as designed; X has no business messing with kernel ram
> over 1Mb, there is nothing there for it to (ab)use.
> (There is PCI memory much higher up but that is allowed again)
See below. I've reduced it to show the critical parts (AFAICS). Please
tell me if I shall mail you the whole unmodified strace -f output from
startx.
It looks like it is scanning /dev/mem page-by-page for some reason trying
to get or identify some 512 page mapping. If /dev/mem does not return
EPERM after 1MB (i.e. with my patch applied), it scans the whole 192MB of
physical memory in the box entirely before it continues.
System is XFree86-Mach64-3.3.6-23mdk running behalf of XFree86-4.1.0-17mdk
with glx support, using a Mach64 RagePro 215GP PCI card.
Btw, if reading from /dev/mem is intended to fail above 1MB, it seems
there might be an off-by-one somewhere, because the read starting at
1048576 (=1024 x 1024) below succeeds. I.e. the first page failing the
read is page 257 on zero-based page counting, not 256.
HTH,
Martin
---------------
2285 fork() = 2286
2286 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
2286 rt_sigaction(SIGTTIN, {SIG_IGN}, {SIG_DFL}, 8) = 0
2286 rt_sigaction(SIGTTOU, {SIG_IGN}, {SIG_DFL}, 8) = 0
2286 rt_sigaction(SIGUSR1, {SIG_IGN}, {0x8049c40, [USR1], SA_RESTART|0x4000000}, 8) = 0
2286 getpid() = 2286
2286 setpgid(0, 2286) = 0
2286 execve("/sbin/X", ["X", ":0", "-deferglyphs", "16"], [/* 37 vars */]) = -1 ENOENT (No such file or directory)
2286 execve("/usr/sbin/X", ["X", ":0", "-deferglyphs", "16"], [/* 37 vars */]) = -1 ENOENT (No such file or directory)
2286 execve("/bin/X", ["X", ":0", "-deferglyphs", "16"], [/* 37 vars */]) = -1 ENOENT (No such file or directory)
2286 execve("/usr/bin/X", ["X", ":0", "-deferglyphs", "16"], [/* 37 vars */]) = -1 ENOENT (No such file or directory)
2286 execve("/usr/X11R6/bin/X", ["X", ":0", "-deferglyphs", "16"], [/* 37 vars */] <unfinished ...>
2286 <... execve resumed> ) = 0
...
2286 write(2, "(--) Mach64: PCI: Mach64 RagePro"..., 107) = 107
2286 iopl(0x3) = 0
2286 open("/dev/mem", O_RDONLY) = 5
2286 lseek(5, 786480, SEEK_SET) = 786480
2286 read(5, " 761295520", 10) = 10
2286 close(5) = 0
2286 open("/dev/mem", O_RDONLY) = 5
2286 lseek(5, 786432, SEEK_SET) = 786432
2286 read(5, "U\252@\353{$/\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0x\1\0\0"..., 65536) = 65536
2286 close(5) = 0
...
2286 write(2, "[mach64] ", 9) = 9
2286 write(2, "Using memory file file: /root/tm"..., 46) = 46
2286 open("/root/tmp/glx_P3SgdqZ", O_RDWR|O_CREAT|O_TRUNC|O_EXCL, 0600) = 5
2286 lseek(5, 2097151, SEEK_SET) = 2097151
2286 write(5, "\0", 1) = 1
2286 old_mmap(NULL, 2097152, PROT_READ|PROT_WRITE, MAP_SHARED, 5, 0) = 0xb7149000
2286 mlock(0xb7149000, 3221223447) = 0
2286 write(2, "[mach64] ", 9) = 9
2286 write(2, "2 megs of scattered memory at vi"..., 49) = 49
2286 write(2, "[mach64] ", 9) = 9
2286 write(2, "Locating 512 pages in VM\n", 25) = 25
2286 gettimeofday({1096010897, 786404}, {0, 0}) = 0
2286 open("/dev/mem", O_RDONLY) = 6
2286 lseek(6, 4096, SEEK_SET) = 4096
2286 read(6, "\211\315\301\351\2\363\245\211", 8) = 8
2286 lseek(6, 8192, SEEK_SET) = 8192
2286 read(6, "\0\0\0\0\0\0\0\0", 8) = 8
2286 lseek(6, 12288, SEEK_SET) = 12288
2286 read(6, "\0\0\0\0\0\0\0\0", 8) = 8
2286 lseek(6, 16384, SEEK_SET) = 16384
2286 read(6, "!l\'\300\0\0\0\0", 8) = 8
...
2286 lseek(6, 1040384, SEEK_SET) = 1040384
2286 read(6, "Award So", 8) = 8
2286 lseek(6, 1044480, SEEK_SET) = 1044480
2286 read(6, "\20/1?\361\0\0\0", 8) = 8
2286 lseek(6, 1048576, SEEK_SET) = 1048576
2286 read(6, "\374\17\1\25B\200*\0", 8) = 8
2286 lseek(6, 1052672, SEEK_SET) = 1052672
2286 read(6, 0xbffff810, 8) = -1 EPERM (Operation not permitted)
2286 write(2, "[mach64] ", 9) = 9
2286 write(2, "read of /dev/mem failed at 0x101"..., 36) = 36
2286 close(6) = 0
2286 write(2, "\nFatal server error:\n", 21) = 21
2286 write(2, "Didn\'t find 512 pages", 21) = 21
2286 write(2, "\n", 1) = 1
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