Fix ppro csum_partial for 1 byte unaligned buffers
Subsystems (2)
PATCH 1/1 Fix ppro csum_partial for 1 byte unaligned buffers
When using sendfile it can happen that csum_partial is called for memory areas that are not aligned to a 2 byte boundary. The ppro optimized i386 checksum code handled this slowly, but read upto 3 bytes over the end of the buffer. When the skb contents are mapped from highmem this can be fatal because the end of the buffer can be unmapped.
This patch fixes this in a simple non intrusive way by handling the possible fault and recovering from it by using a tolerant byte-by-byte copy. It does not attempt to align one byte unaligned buffers, because that's rather complicated and probably not worth the effort.
Other architectures may want to audit their csum_partial if it handles this case correctly.
Bug is in 2.4 and 2.6
-Andi
arch/i386/lib/checksum.S renamed from arch/i386/lib/checksum.S-o +25 -3
@@ -48,6 +48,9 @@ * least a twofold speedup on 486 and Pentium if it is 4-byte aligned. * Fortunately, it is easy to convert 2-byte alignment to 4-byte * alignment for the unrolled loop. + * + * Danger, Will Robinson: with sendfile 2 byte alignment is not guaranteed. + * */ csum_partial: pushl %esi
@@ -237,18 +240,37 @@ movl $0xffffff,%ebx # by the shll and shrl instructions shll $3,%ecx shrl %cl,%ebx - andl -128(%esi),%ebx # esi is 4-aligned so should be ok +.Ltail: + andl -128(%esi),%ebx +.Ttail_finished addl %ebx,%eax adcl $0,%eax 80: testl $1, 12(%esp) jz 90f roll $8, %eax -90: +90: popl %ebx popl %esi ret - + + .section __ex_table,"a" + .long .Ltail,tail_recover + .long .Ltail_byte3,.Ltail_byte1 + .long .Ltail_byte2,.Ltail_finished + .previous + +tail_recover: + xorl %ebx,%ebx +.Ltail_byte3: + movb -126(%esi),%bl + shl $16,%ebx +.Ltail_byte1: + movb -128(%esi),%bl +.Ltail_byte2: + movb -127(%esi),%bh + jmp .Ltailfinished + #endif /*