Messages in this thread | | | Subject | Re: [PATCH v4] powerpc: Do not make the entire heap executable | From | Denys Vlasenko <> | Date | Mon, 22 Aug 2016 20:37:05 +0200 |
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On 08/21/2016 05:47 PM, Aneesh Kumar K.V wrote: > Denys Vlasenko <dvlasenk@redhat.com> writes: > >> On 32-bit powerpc the ELF PLT sections of binaries (built with --bss-plt, >> or with a toolchain which defaults to it) look like this: >> >> [17] .sbss NOBITS 0002aff8 01aff8 000014 00 WA 0 0 4 >> [18] .plt NOBITS 0002b00c 01aff8 000084 00 WAX 0 0 4 >> [19] .bss NOBITS 0002b090 01aff8 0000a4 00 WA 0 0 4 >> >> Which results in an ELF load header: >> >> Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align >> LOAD 0x019c70 0x00029c70 0x00029c70 0x01388 0x014c4 RWE 0x10000 >> >> This is all correct, the load region containing the PLT is marked as >> executable. Note that the PLT starts at 0002b00c but the file mapping ends at >> 0002aff8, so the PLT falls in the 0 fill section described by the load header, >> and after a page boundary. >> >> Unfortunately the generic ELF loader ignores the X bit in the load headers >> when it creates the 0 filled non-file backed mappings. It assumes all of these >> mappings are RW BSS sections, which is not the case for PPC. >> >> gcc/ld has an option (--secure-plt) to not do this, this is said to incur >> a small performance penalty. >> >> Currently, to support 32-bit binaries with PLT in BSS kernel maps *entire >> brk area* with executable rights for all binaries, even --secure-plt ones. > > > Is this going to break any application ? I am asking because you > mentioned the patch is lightly tested.
I booted powerpc64 machine with RHEL7 installation, it did not catch fire.
> x86 do have a > > #define VM_DATA_DEFAULT_FLAGS \ > (((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0 ) | \ > VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC) > > ie, it can force a read implies exec mode. Do we need that ?
powerpc64 never had that. 32-bit mode may need it, since before this patch all 32-bit tasks were unconditionally getting VM_DATA_DEFAULT_FLAGS with VM_EXEC bit.
I'll send an updated patch.
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