forked from luck/tmp_suning_uos_patched
df513e2cdd
On x86, bit operations operate on a string of bits that can reside in multiple words. For example, 'btsl %eax, (blah)' will touch the word at blah+4 if %eax is between 32 and 63. The x86 emulator compensates for that by advancing the operand address by (bit offset / BITS_PER_LONG) and truncating the bit offset to the range (0..BITS_PER_LONG-1). This has a side effect of forcing the operand size to 8 bytes on 64-bit hosts. Now, a 32-bit guest goes and fork()s a process. It write protects a stack page at 0xbffff000 using the 'btr' instruction, at offset 0xffc in the page table, with bit offset 1 (for the write permission bit). The emulator now forces the operand size to 8 bytes as previously described, and an innocent page table update turns into a cross-page-boundary write, which is assumed by the mmu code not to be a page table, so it doesn't actually clear the corresponding shadow page table entry. The guest and host permissions are out of sync and guest memory is corrupted soon afterwards, leading to guest failure. Fix by not using BITS_PER_LONG as the word size; instead use the actual operand size, so we get a 32-bit write in that case. Note we still have to teach the mmu to handle cross-page-boundary writes to guest page table; but for now this allows Damn Small Linux 0.4 (2.4.20) to boot. Signed-off-by: Avi Kivity <avi@qumranet.com> |
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| .. | ||
| Kconfig | ||
| kvm_main.c | ||
| kvm_svm.h | ||
| kvm_vmx.h | ||
| kvm.h | ||
| Makefile | ||
| mmu.c | ||
| paging_tmpl.h | ||
| segment_descriptor.h | ||
| svm.c | ||
| svm.h | ||
| vmx.c | ||
| vmx.h | ||
| x86_emulate.c | ||
| x86_emulate.h | ||