Re: [PATCH v4 3.0-rc2-tip 2/22] 2: uprobes: Breakground page replacement.
From: Peter Zijlstra <peterz@infradead.org>
Date: 2011-06-14 12:58:46
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On Mon, 2011-06-13 at 14:29 +0530, Srikar Dronamraju wrote:
* Peter Zijlstra [off-list ref] [2011-06-10 01:03:29]:quoted
On Tue, 2011-06-07 at 18:28 +0530, Srikar Dronamraju wrote:quoted
+ vaddr_old = kmap_atomic(old_page, KM_USER0); + vaddr_new = kmap_atomic(new_page, KM_USER1); + + memcpy(vaddr_new, vaddr_old, PAGE_SIZE); + /* poke the new insn in, ASSUMES we don't cross page boundary */ + addr = vaddr; + vaddr &= ~PAGE_MASK; + memcpy(vaddr_new + vaddr, &opcode, uprobe_opcode_sz); + + kunmap_atomic(vaddr_new); + kunmap_atomic(vaddr_old);quoted
+ vaddr_new = kmap_atomic(page, KM_USER0); + vaddr &= ~PAGE_MASK; + memcpy(opcode, vaddr_new + vaddr, uprobe_opcode_sz); + kunmap_atomic(vaddr_new);quoted
Both sequences in resp {write,read}_opcode() assume the opcode doesn't cross page boundaries but don't in fact have any assertions validating this assumption.read_opcode and write_opcode reads/writes just one breakpoint instruction I had the below note just above the write_opcode definition. /* * NOTE: * Expect the breakpoint instruction to be the smallest size instruction for * the architecture. If an arch has variable length instruction and the * breakpoint instruction is not of the smallest length instruction * supported by that architecture then we need to modify read_opcode / * write_opcode accordingly. This would never be a problem for archs that * have fixed length instructions. */
Whoever reads comments anyway? :-)
Do we have archs which have a breakpoint instruction which isnt of the smallest instruction size for that arch. If we do have can we change the write_opcode/read_opcode while we support that architecture?
Why not put a simple WARN_ON_ONCE() in there that checks the assumption? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>