Date: Sat, 20 Apr 2019 11:38:58 +0000 From: Joel Fernandes <joel@...lfernandes.org> To: Jessica Yu <jeyu@...nel.org> Cc: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com, keescook@...omium.org, mathieu.desnoyers@...icios.com, kernel-hardening@...ts.openwall.com, kernel-team@...roid.com, rcu@...r.kernel.org Subject: Re: [PATCH v3 3/3] module: Make __tracepoints_ptrs as read-only On Wed, Apr 17, 2019 at 05:16:18PM +0200, Jessica Yu wrote: > +++ Steven Rostedt [10/04/19 20:44 -0400]: > > On Wed, 10 Apr 2019 16:29:02 -0400 > > Joel Fernandes <joel@...lfernandes.org> wrote: > > > > > The srcu structure pointer array is modified at module load time because the > > > array is fixed up by the module loader at load-time with the final locations > > > of the tracepoints right? Basically relocation fixups. At compile time, I > > > believe it is not know what the values in the ptr array are. I believe same > > > is true for the tracepoint ptrs array. > > > > > > Also it needs to be in a separate __tracepoint_ptrs so that this code works: > > > > > > > > > #ifdef CONFIG_TRACEPOINTS > > > mod->tracepoints_ptrs = section_objs(info, "__tracepoints_ptrs", > > > sizeof(*mod->tracepoints_ptrs), > > > &mod->num_tracepoints); > > > #endif > > > > > > Did I miss some point? Thanks, > > > > But there's a lot of others too. Hmm, does this mean that the RO data > > sections that are in modules are not set to RO? > > > > There's a bunch of separate sections that are RO. Just look in > > include/asm-generic/vmlinux.lds.h under the RO_DATA_SECTION() macro. > > > > A lot of the sections saved in module.c:find_module_sections() are in > > that RO_DATA when compiled as a builtin. Are they not RO when loaded via > > a module? > > Unlike the kernel, the module loader does not rely on a linker script > to determine which sections get what protections. On module load, all > sections in a module are looped through and those sections without the > SHF_WRITE flag will be set to RO. For example, when there is a section > filled with structs declared as const or if the section was explicitly > given only the SHF_ALLOC attribute, those will be read-only. As long > as the sections were given the correct section attributes for > read-only, it'll have read-only protection. I see this is already the > case for __param and __ksymtab*/__kcrctab* sections, but I agree that > a full audit would be useful to be consistent with builtin RO > protections. Thanks a lot for the explanations. Yes we dropped the patches because const worked. This is good to know for future such ventures as well ;-) Best, - Joel > Jessica
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