Date: Thu, 30 May 2019 13:49:10 -0400 From: sva sva <azharivs@...il.com> To: musl@...ts.openwall.com Subject: Re: How to get base address of heap arenas Indeed your replies verified my understanding. Here's what I want to do: I have a C library that does malloc interposition and adds signatures to header and footer of chunks by allocating extra bytes before and after it. It also does a number of other things. Then I have some C code which is supposed to walk the entire heap to that particular process and spit out all the heap signatures making sure there are no scribbled ones. What I am doing right now is that whenever I get a malloc/calloc/etc., which is of course overloaded, I follow the returned pointer all the way back to reach the top chunk (prev size = 0). This would fail when I get chunks in different memory regions that are not contiguous. So I need to somehow keep track of the contiguous heap areas and get the top chunk for all of those to start my heap walk. Last thing I want to do is to patch musl's libc. Thanks Vahid On Thu, May 30, 2019 at 10:02 AM Rich Felker <dalias@...c.org> wrote: > On Thu, May 30, 2019 at 03:27:24PM +0200, Szabolcs Nagy wrote: > > * sva sva <azharivs@...il.com> [2019-05-30 08:59:46 -0400]: > > > I am writing a heap walk program in C and would like to know if there > is > > > anything like the concept of arenas in musl. Basically, I need to have > a > > > pointer to the base address of all my allocated heaps. Unfortunately > > > inspecting the musl code I found none. > > > > there is no such concept as "heap arena" visible to user > > code, so almost surely you don't "need a pointer to the > > base address" of it. > > > > try to describe what exactly you want to do (not in terms > > of libc internals, but in terms that make sense for user > > code) > > > > (do you want to get all memory mappings? -> try /proc/self/maps) > > (do you want to track malloc behaviour? -> try malloc interposition) > > (etc) > > To further clarify, the current allocator implementation has no global > view of "the heap". It sees only free chunks and the headers or > footers of the immediately adjacent-in-address-space allocated chunks. > It's likely that the future replacement will have global tracking that > further helps ensure integrity against heap corruption attacks, but it > won't be a public API or something necessarily stable between > versions. If you want a debugging malloc, you need to interpose one; > for the past few releases, musl has supported malloc interposition. > > Rich > Content of type "text/html" skipped
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