Re: [PATCH v2 0/2] Fix issue with alternatives/paravirt patches
On Thu, Jul 21, 2016 at 01:23:58AM -0400, Jessica Yu wrote: > Hi, > > A few months ago, Chris Arges reported a bug involving alternatives/paravirt > patching that was discussed here [1] and here [2]. To briefly summarize the > bug, patch modules that contained .altinstructions or .parainstructions > sections would break because these alternative/paravirt patches would be > applied first by the module loader (see x86 module_finalize()), then > livepatch would later clobber these patches when applying per-object > relocations. This lead to crashes and unpredictable behavior. > > One conclusion we reached from our last discussion was that we will > need to introduce some arch-specific code to address this problem. > This patchset presents a possible fix for the bug by adding a new > arch-specific arch_klp_init_object_loaded() function that by default > does nothing but can be overridden by different arches. > > To fix this issue for x86, since we can access a patch module's Elf > sections through mod->klp_info, we can simply delay the calls to > apply_paravirt() and apply_alternatives() to arch_klp_init_object_loaded(), > which is called after relocations have been written for an object. > In addition, for patch modules, .parainstructions and .altinstructions are > prefixed by ".klp.arch.${objname}" so that the module loader ignores them > and livepatch can apply them manually. > > Currently for kpatch, we don't support including jump table sections in > the patch module, and supporting .smp_locks is currently broken, so we > don't consider those sections (for now). > > I did some light testing with some patches to kvm and verified that the > original issue reported in [2] was fixed. > > Based on linux-next. For the series: Acked-by: Josh Poimboeuf -- Josh
[PATCH v2 0/2] Fix issue with alternatives/paravirt patches
Hi, A few months ago, Chris Arges reported a bug involving alternatives/paravirt patching that was discussed here [1] and here [2]. To briefly summarize the bug, patch modules that contained .altinstructions or .parainstructions sections would break because these alternative/paravirt patches would be applied first by the module loader (see x86 module_finalize()), then livepatch would later clobber these patches when applying per-object relocations. This lead to crashes and unpredictable behavior. One conclusion we reached from our last discussion was that we will need to introduce some arch-specific code to address this problem. This patchset presents a possible fix for the bug by adding a new arch-specific arch_klp_init_object_loaded() function that by default does nothing but can be overridden by different arches. To fix this issue for x86, since we can access a patch module's Elf sections through mod->klp_info, we can simply delay the calls to apply_paravirt() and apply_alternatives() to arch_klp_init_object_loaded(), which is called after relocations have been written for an object. In addition, for patch modules, .parainstructions and .altinstructions are prefixed by ".klp.arch.${objname}" so that the module loader ignores them and livepatch can apply them manually. Currently for kpatch, we don't support including jump table sections in the patch module, and supporting .smp_locks is currently broken, so we don't consider those sections (for now). I did some light testing with some patches to kvm and verified that the original issue reported in [2] was fixed. Based on linux-next. v1 here: http://lkml.kernel.org/g/1467772500-26092-1-git-send-email-j...@redhat.com v2: - add BUILD_BUG_ON() check in arch_klp_init_object_loaded (x86) [1] http://thread.gmane.org/gmane.linux.kernel/2185604/ [2] https://github.com/dynup/kpatch/issues/580 Jessica Yu (2): livepatch: use arch_klp_init_object_loaded() to finish arch-specific tasks livepatch/x86: apply alternatives and paravirt patches after relocations arch/x86/kernel/Makefile| 1 + arch/x86/kernel/livepatch.c | 65 + include/linux/livepatch.h | 3 +++ kernel/livepatch/core.c | 12 +++-- 4 files changed, 79 insertions(+), 2 deletions(-) create mode 100644 arch/x86/kernel/livepatch.c -- 2.5.5