Date: Fri, 17 Apr 2015 16:19:54 -0400 From: Yue Chen <ychen.contact@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-arch@freebsd.org Subject: Re: Situations about PC values in kernel data segments Message-ID: <CAKtBrB5Md0o-ERVBkLii11SROWXZd7HXUt=9Kk_verANb%2BKPVw@mail.gmail.com> In-Reply-To: <6048769.xVxqkDkTGK@ralph.baldwin.cx> References: <CAKtBrB6g5fR_tvT=KwrER4_VGfYB-fF-2DWmm1vMDpZ55qb2qg@mail.gmail.com> <6048769.xVxqkDkTGK@ralph.baldwin.cx>
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I mean, the PC values in non-.text segments like .data, .rodata, stack, heap, etc. Usually this is for comparison purposes. E.g., compare the faulting PC against some range already stored in a table/handler. > When pcb_onfault is used it is set to point to code in a .text segment, not anywhere else. The pointer value stored in non-.text segments is a PC value (instruction address in .text), like 0xffffffff12345678, and may not be a function entry point address, right? On Fri, Apr 17, 2015 at 9:22 AM, John Baldwin <jhb@freebsd.org> wrote: > On Saturday, April 11, 2015 05:18:28 AM Yue Chen wrote: > > Dear all, > > > > We are working on a project about OS security. > > We wonder in which situations the program counter (PC) value (e.g., the > > value in %RIP on x86_64, i.e, instruction address) could be in kernel > > (module) data segments (including stack, heap, etc.). > > > > Here we mainly care about the address/value that are NOT function entry > > points since there exist a number of function pointers. Also, we only > > consider the normal cases because one can write arbitrary values into a > > variable/pointer. And we mainly consider i386, AMD64 and ARM. > > > > Here are some situations I can think about: > > function/interrupt/exception/syscall return address on stack; switch/case > > jump table target; page fault handler (pcb_onfault on *BSD); restartable > > atomic sequences (RAS) registry; thread/process context structure like > Task > > state segment (TSS), process control block (PCB) and thread control block > > (TCB); situations for debugging purposes (e.g., like those in ``segment > not > > present'' exception handler). > > > > Additionally, does any of these addresses have offset formats or special > > encodings? For example, on x86_64, we may use 32-bit RIP-relative > > (addressing) offset to represent a 64-bit full address. In glibc's > > setjmp/longjmp jmp_buf, they use a special encoding (PTR_MANGLE) for > saved > > register values. > > For i386 and amd64, I think all of the code that is executed does live in a > .text segment. When pcb_onfault is used it is set to point to code in a > .text > segment, not anywhere else. Similarly, fault and exception handlers as > well > as the stub for new threads/processes after fork/thread_create is in .text > as well. There are multiple text segments present when modules are loaded > of course, but you should be able to enumerate all of those in the linker. > > -- > John Baldwin >
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