Messages in this thread Patch in this message | | | From | Bjorn Helgaas <> | Subject | [RFC] prevent "dd if=/dev/mem" crash | Date | Fri, 17 Oct 2003 16:10:36 -0600 |
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This is the generic part of a change to prevent "dd if=/dev/mem" from causing a machine check on ia64.
read_mem() and write_mem() already check the requested address against "high_memory", but that is only a complete check if everything from 0 to high_memory is valid, readable/writable memory. Obviously that's not the case for architectures with discontiguous memory, like ia64.
Old behavior:
# dd if=/dev/mem of=/dev/null <unrecoverable machine check>
New behavior (this system has a hole from 0-16MB, then memory from 16MB-1GB):
# dd if=/dev/mem of=/dev/null 0+0 records in 0+0 records out 0 bytes transferred in 0.000282 seconds (0 bytes/sec)
# dd if=/dev/mem of=/dev/null bs=1M skip=16 1004+10 records in 1004+10 records out 1056964608 bytes transferred in 1.629262 seconds (648738280 bytes/sec)
I expect there are probably different opinions about the idea that "dd if=/dev/mem" exits without doing anything. Sparc and 68K have nearby code that bit-buckets writes and returns zeroes for reads of page zero. We could do that, too, but it seems like kind of a hack, and holes on ia64 can be BIG (on the order of 256GB for one box).
So flame away :-)
The patch below is mangled so it won't apply easily. If this seems a reasonable approach, I'll submit the ia64 piece first, then repost this.
Bjorn
===== drivers/char/mem.c 1.44 vs edited ===== --- 1.44/ drivers/char/mem.c Sun Sep 21 15:50:34 2003 +++ edited/ drivers/char/mem.c Fri Oct 17 15:37:47 2003 @@ -79,6 +79,24 @@ #endif } +static inline int valid_mem_range(unsigned long addr, size_t *count) +{ +#if defined(CONFIG_IA64) + return efi_valid_mem_range(addr, count); +#else + unsigned long end_mem; + + end_mem = __pa(high_memory); + if (addr >= end_mem) + return 0; + + if (*count > end_mem - addr) + *count = end_mem - addr; + + return 1; +#endif +} + static ssize_t do_write_mem(struct file * file, void *p, unsigned long realp, const char * buf, size_t count, loff_t *ppos) { @@ -113,14 +131,10 @@ size_t count, loff_t *ppos) { unsigned long p = *ppos; - unsigned long end_mem; ssize_t read; - end_mem = __pa(high_memory); - if (p >= end_mem) + if (!valid_mem_range(p, &count)) return 0; - if (count > end_mem - p) - count = end_mem - p; read = 0; #if defined(__sparc__) || (defined(__mc68000__) && defined(CONFIG_MMU)) /* we don't have page 0 mapped on sparc and m68k.. */ @@ -149,13 +163,9 @@ size_t count, loff_t *ppos) { unsigned long p = *ppos; - unsigned long end_mem; - end_mem = __pa(high_memory); - if (p >= end_mem) + if (!valid_mem_range(p, &count)) return 0; - if (count > end_mem - p) - count = end_mem - p; return do_write_mem(file, __va(p), p, buf, count, ppos); } ===== include/linux/efi.h 1.3 vs edited ===== --- 1.3/ include/linux/efi.h Thu Aug 7 14:01:48 2003 +++ edited/ include/linux/efi.h Thu Oct 16 16:54:52 2003 @@ -266,6 +266,7 @@ extern u64 efi_get_iobase (void); extern u32 efi_mem_type (unsigned long phys_addr); extern u64 efi_mem_attributes (unsigned long phys_addr); +extern int efi_valid_mem_range (unsigned long phys_addr, unsigned long *count); /* * Variable Attributes - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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