Messages in this thread | | | From | Dmitry Vyukov <> | Date | Tue, 1 Oct 2019 05:01:58 +0200 | Subject | Re: [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN_GENERIC=y |
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On Tue, Oct 1, 2019 at 4:36 AM Walter Wu <walter-zh.wu@mediatek.com> wrote: > > On Mon, 2019-09-30 at 10:57 +0200, Marc Gonzalez wrote: > > On 30/09/2019 06:36, Walter Wu wrote: > > > > > bool check_memory_region(unsigned long addr, size_t size, bool write, > > > unsigned long ret_ip) > > > { > > > + if (long(size) < 0) { > > > + kasan_report_invalid_size(src, dest, len, _RET_IP_); > > > + return false; > > > + } > > > + > > > return check_memory_region_inline(addr, size, write, ret_ip); > > > } > > > > Is it expected that memcpy/memmove may sometimes (incorrectly) be passed > > a negative value? (It would indeed turn up as a "large" size_t) > > > > IMO, casting to long is suspicious. > > > > There seem to be some two implicit assumptions. > > > > 1) size >= ULONG_MAX/2 is invalid input > > 2) casting a size >= ULONG_MAX/2 to long yields a negative value > > > > 1) seems reasonable because we can't copy more than half of memory to > > the other half of memory. I suppose the constraint could be even tighter, > > but it's not clear where to draw the line, especially when considering > > 32b vs 64b arches. > > > > 2) is implementation-defined, and gcc works "as expected" (clang too > > probably) https://gcc.gnu.org/onlinedocs/gcc/Integers-implementation.html > > > > A comment might be warranted to explain the rationale. > > Regards. > > Thanks for your suggestion. > Yes, It is passed a negative value issue in memcpy/memmove/memset. > Our current idea should be assumption 1 and only consider 64b arch, > because KASAN only supports 64b. In fact, we really can't use so much > memory in 64b arch. so assumption 1 make sense.
Note there are arm KASAN patches floating around, so we should not make assumptions about 64-bit arch.
But there seems to be a number of such casts already:
$ find -name "*.c" -exec egrep "\(long\).* < 0" {} \; -print } else if ((long) delta < 0) { ./kernel/time/timer.c if ((long)state < 0) ./drivers/thermal/thermal_sysfs.c if ((long)delay < 0) ./drivers/infiniband/core/addr.c if ((long)tmo < 0) ./drivers/net/wireless/st/cw1200/pm.c if (pos < 0 || (long) pos != pos || (ssize_t) count < 0) ./sound/core/info.c if ((long)hwrpb->sys_type < 0) { ./arch/alpha/kernel/setup.c if ((long)m->driver_data < 0) ./arch/x86/kernel/apic/apic.c if ((long) size < 0L) if ((long)addr < 0L) { ./arch/sparc/mm/init_64.c if ((long)lpid < 0) ./arch/powerpc/kvm/book3s_hv.c if ((long)regs->regs[insn.mm_i_format.rs] < 0) if ((long)regs->regs[insn.i_format.rs] < 0) { if ((long)regs->regs[insn.i_format.rs] < 0) { ./arch/mips/kernel/branch.c if ((long)arch->gprs[insn.i_format.rs] < 0) if ((long)arch->gprs[insn.i_format.rs] < 0) ./arch/mips/kvm/emulate.c if ((long)regs->regs[insn.i_format.rs] < 0) ./arch/mips/math-emu/cp1emu.c if ((int32_t)(long)prom_vec < 0) { ./arch/mips/sibyte/common/cfe.c if (msgsz > ns->msg_ctlmax || (long) msgsz < 0 || msqid < 0) if (msqid < 0 || (long) bufsz < 0) ./ipc/msg.c if ((long)x < 0) ./mm/page-writeback.c if ((long)(next - val) < 0) { ./mm/memcontrol.c
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