Re: [PATCH bpf-next v2 0/3] bpf: add boot parameters for sysctl knobs
On Fri, May 25, 2018 at 06:50:09PM +0200, Eugene Syromiatnikov wrote: > On Thu, May 24, 2018 at 04:34:51PM -0700, Alexei Starovoitov wrote: > > On Thu, May 24, 2018 at 09:41:08AM +0200, Jesper Dangaard Brouer wrote: > > > On Wed, 23 May 2018 15:02:45 -0700 > > > Alexei Starovoitovwrote: > > > > > > > On Wed, May 23, 2018 at 02:18:19PM +0200, Eugene Syromiatnikov wrote: > > > > > Some BPF sysctl knobs affect the loading of BPF programs, and during > > > > > system boot/init stages these sysctls are not yet configured. > > > > > A concrete example is systemd, that has implemented loading of BPF > > > > > programs. > > > > > > > > > > Thus, to allow controlling these setting at early boot, this patch set > > > > > adds the ability to change the default setting of these sysctl knobs > > > > > as well as option to override them via a boot-time kernel parameter > > > > > (in order to avoid rebuilding kernel each time a need of changing > > > > > these > > > > > defaults arises). > > > > > > > > > > The sysctl knobs in question are kernel.unprivileged_bpf_disable, > > > > > net.core.bpf_jit_harden, and net.core.bpf_jit_kallsyms. > > > > > > > > - systemd is root. today it only uses cgroup-bpf progs which require > > > > root, > > > > so disabling unpriv during boot time makes no difference to systemd. > > > > what is the actual reason to present time? > systemd also runs a lot of code, some of which is unprivileged. systemd processes sysctl configs first. It's essential for system security to do so. If you have concerns in how systemd does that please bring it up with systemd folks. > > > > - say in the future systemd wants to use so_reuseport+bpf for faster > > > > networking. With unpriv disable during boot, it will force systemd > > > > to do such networking from root, which will lower its security > > > > barrier. > No, it will force systemd not to use SO_REUSEPORT BPF. sorry this argument makes no sense to me. > > > > - bpf_jit_kallsyms sysctl has immediate effect on loaded programs. > > > > Flipping it during the boot or right after or any time after > > > > is the same thing. Why add such boot flag then? > Well, that one was for completeness. Should we convert all sysctls to bootparams for 'completeness' ? > > > > - jit_harden can be turned on by systemd. so turning it during the boot > > > > will make systemd progs to be constant blinded. > > > > Constant blinding protects kernel from unprivileged JIT spraying. > > > > Are you worried that systemd will attack the kernel with JIT spraying? > I'm worried that systemd can be exploited for a JIT spraying attack. I'm afraid we're not on the same page with definition of 'JIT spraying attack'. > Another thing I'm concerned with is that the generated code is different, > which introduces additional complication during debugging. specifically what kind of complication? -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH bpf-next v2 0/3] bpf: add boot parameters for sysctl knobs
On Thu, May 24, 2018 at 04:34:51PM -0700, Alexei Starovoitov wrote: > On Thu, May 24, 2018 at 09:41:08AM +0200, Jesper Dangaard Brouer wrote: > > On Wed, 23 May 2018 15:02:45 -0700 > > Alexei Starovoitovwrote: > > > > > On Wed, May 23, 2018 at 02:18:19PM +0200, Eugene Syromiatnikov wrote: > > > > Some BPF sysctl knobs affect the loading of BPF programs, and during > > > > system boot/init stages these sysctls are not yet configured. > > > > A concrete example is systemd, that has implemented loading of BPF > > > > programs. > > > > > > > > Thus, to allow controlling these setting at early boot, this patch set > > > > adds the ability to change the default setting of these sysctl knobs > > > > as well as option to override them via a boot-time kernel parameter > > > > (in order to avoid rebuilding kernel each time a need of changing these > > > > defaults arises). > > > > > > > > The sysctl knobs in question are kernel.unprivileged_bpf_disable, > > > > net.core.bpf_jit_harden, and net.core.bpf_jit_kallsyms. > > > > > > - systemd is root. today it only uses cgroup-bpf progs which require root, > > > so disabling unpriv during boot time makes no difference to systemd. > > > what is the actual reason to present time? systemd also runs a lot of code, some of which is unprivileged. > > > - say in the future systemd wants to use so_reuseport+bpf for faster > > > networking. With unpriv disable during boot, it will force systemd > > > to do such networking from root, which will lower its security barrier. No, it will force systemd not to use SO_REUSEPORT BPF. > > > - bpf_jit_kallsyms sysctl has immediate effect on loaded programs. > > > Flipping it during the boot or right after or any time after > > > is the same thing. Why add such boot flag then? Well, that one was for completeness. > > > - jit_harden can be turned on by systemd. so turning it during the boot > > > will make systemd progs to be constant blinded. > > > Constant blinding protects kernel from unprivileged JIT spraying. > > > Are you worried that systemd will attack the kernel with JIT spraying? I'm worried that systemd can be exploited for a JIT spraying attack. Another thing I'm concerned with is that the generated code is different, which introduces additional complication during debugging. > > I think you are missing that, we want the ability to change these > > defaults in-order to avoid depending on /etc/sysctl.conf settings, and > > that the these sysctl.conf setting happen too late. > > What does it mean 'happens too late' ? > Too late for what? > sysctl.conf has plenty of system critical knobs like > kernel.perf_event_paranoid, kernel.core_pattern, etc > The behavior of the host is drastically different after sysctl config > is applied. > > > For example with jit_harden, there will be a difference between the > > loaded BPF program that got loaded at boot-time with systemd (no > > constant blinding) and when someone reloads that systemd service after > > /etc/sysctl.conf have been evaluated and setting bpf_jit_harden (now > > slower due to constant blinding). This is inconsistent behavior. > > net.core.bpf_jit_harden can be flipped back and forth at run-time, > so bpf progs before and after will be either blinded or not. > I don't see any inconsistency. That can't be the reason to maintain that inconsistency. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH bpf-next v2 0/3] bpf: add boot parameters for sysctl knobs
On Thu, May 24, 2018 at 09:41:08AM +0200, Jesper Dangaard Brouer wrote: > On Wed, 23 May 2018 15:02:45 -0700 > Alexei Starovoitovwrote: > > > On Wed, May 23, 2018 at 02:18:19PM +0200, Eugene Syromiatnikov wrote: > > > Some BPF sysctl knobs affect the loading of BPF programs, and during > > > system boot/init stages these sysctls are not yet configured. > > > A concrete example is systemd, that has implemented loading of BPF > > > programs. > > > > > > Thus, to allow controlling these setting at early boot, this patch set > > > adds the ability to change the default setting of these sysctl knobs > > > as well as option to override them via a boot-time kernel parameter > > > (in order to avoid rebuilding kernel each time a need of changing these > > > defaults arises). > > > > > > The sysctl knobs in question are kernel.unprivileged_bpf_disable, > > > net.core.bpf_jit_harden, and net.core.bpf_jit_kallsyms. > > > > - systemd is root. today it only uses cgroup-bpf progs which require root, > > so disabling unpriv during boot time makes no difference to systemd. > > what is the actual reason to present time? > > > > - say in the future systemd wants to use so_reuseport+bpf for faster > > networking. With unpriv disable during boot, it will force systemd > > to do such networking from root, which will lower its security barrier. > > How that make sense? > > > > - bpf_jit_kallsyms sysctl has immediate effect on loaded programs. > > Flipping it during the boot or right after or any time after > > is the same thing. Why add such boot flag then? > > > > - jit_harden can be turned on by systemd. so turning it during the boot > > will make systemd progs to be constant blinded. > > Constant blinding protects kernel from unprivileged JIT spraying. > > Are you worried that systemd will attack the kernel with JIT spraying? > > > I think you are missing that, we want the ability to change these > defaults in-order to avoid depending on /etc/sysctl.conf settings, and > that the these sysctl.conf setting happen too late. What does it mean 'happens too late' ? Too late for what? sysctl.conf has plenty of system critical knobs like kernel.perf_event_paranoid, kernel.core_pattern, etc The behavior of the host is drastically different after sysctl config is applied. > For example with jit_harden, there will be a difference between the > loaded BPF program that got loaded at boot-time with systemd (no > constant blinding) and when someone reloads that systemd service after > /etc/sysctl.conf have been evaluated and setting bpf_jit_harden (now > slower due to constant blinding). This is inconsistent behavior. net.core.bpf_jit_harden can be flipped back and forth at run-time, so bpf progs before and after will be either blinded or not. I don't see any inconsistency. In general I think bootparams should be used only for things like kpti=on/off that cannot be set by sysctl. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH bpf-next v2 0/3] bpf: add boot parameters for sysctl knobs
On Wed, 23 May 2018 15:02:45 -0700 Alexei Starovoitovwrote: > On Wed, May 23, 2018 at 02:18:19PM +0200, Eugene Syromiatnikov wrote: > > Some BPF sysctl knobs affect the loading of BPF programs, and during > > system boot/init stages these sysctls are not yet configured. > > A concrete example is systemd, that has implemented loading of BPF > > programs. > > > > Thus, to allow controlling these setting at early boot, this patch set > > adds the ability to change the default setting of these sysctl knobs > > as well as option to override them via a boot-time kernel parameter > > (in order to avoid rebuilding kernel each time a need of changing these > > defaults arises). > > > > The sysctl knobs in question are kernel.unprivileged_bpf_disable, > > net.core.bpf_jit_harden, and net.core.bpf_jit_kallsyms. > > - systemd is root. today it only uses cgroup-bpf progs which require root, > so disabling unpriv during boot time makes no difference to systemd. > what is the actual reason to present time? > > - say in the future systemd wants to use so_reuseport+bpf for faster > networking. With unpriv disable during boot, it will force systemd > to do such networking from root, which will lower its security barrier. > How that make sense? > > - bpf_jit_kallsyms sysctl has immediate effect on loaded programs. > Flipping it during the boot or right after or any time after > is the same thing. Why add such boot flag then? > > - jit_harden can be turned on by systemd. so turning it during the boot > will make systemd progs to be constant blinded. > Constant blinding protects kernel from unprivileged JIT spraying. > Are you worried that systemd will attack the kernel with JIT spraying? I think you are missing that, we want the ability to change these defaults in-order to avoid depending on /etc/sysctl.conf settings, and that the these sysctl.conf setting happen too late. For example with jit_harden, there will be a difference between the loaded BPF program that got loaded at boot-time with systemd (no constant blinding) and when someone reloads that systemd service after /etc/sysctl.conf have been evaluated and setting bpf_jit_harden (now slower due to constant blinding). This is inconsistent behavior. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH bpf-next v2 0/3] bpf: add boot parameters for sysctl knobs
On Wed, May 23, 2018 at 02:18:19PM +0200, Eugene Syromiatnikov wrote: > Some BPF sysctl knobs affect the loading of BPF programs, and during > system boot/init stages these sysctls are not yet configured. > A concrete example is systemd, that has implemented loading of BPF > programs. > > Thus, to allow controlling these setting at early boot, this patch set > adds the ability to change the default setting of these sysctl knobs > as well as option to override them via a boot-time kernel parameter > (in order to avoid rebuilding kernel each time a need of changing these > defaults arises). > > The sysctl knobs in question are kernel.unprivileged_bpf_disable, > net.core.bpf_jit_harden, and net.core.bpf_jit_kallsyms. - systemd is root. today it only uses cgroup-bpf progs which require root, so disabling unpriv during boot time makes no difference to systemd. what is the actual reason to present time? - say in the future systemd wants to use so_reuseport+bpf for faster networking. With unpriv disable during boot, it will force systemd to do such networking from root, which will lower its security barrier. How that make sense? - bpf_jit_kallsyms sysctl has immediate effect on loaded programs. Flipping it during the boot or right after or any time after is the same thing. Why add such boot flag then? - jit_harden can be turned on by systemd. so turning it during the boot will make systemd progs to be constant blinded. Constant blinding protects kernel from unprivileged JIT spraying. Are you worried that systemd will attack the kernel with JIT spraying? -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH bpf-next v2 0/3] bpf: add boot parameters for sysctl knobs
Some BPF sysctl knobs affect the loading of BPF programs, and during system boot/init stages these sysctls are not yet configured. A concrete example is systemd, that has implemented loading of BPF programs. Thus, to allow controlling these setting at early boot, this patch set adds the ability to change the default setting of these sysctl knobs as well as option to override them via a boot-time kernel parameter (in order to avoid rebuilding kernel each time a need of changing these defaults arises). The sysctl knobs in question are kernel.unprivileged_bpf_disable, net.core.bpf_jit_harden, and net.core.bpf_jit_kallsyms. Eugene Syromiatnikov (3): bpf: add ability to configure unprivileged BPF via boot-time parameter bpf: add ability to configure BPF JIT hardening via boot-time parameter bpf: add ability to configure BPF JIT kallsyms export at the boot time Documentation/admin-guide/kernel-parameters.txt | 28 init/Kconfig| 90 + kernel/bpf/core.c | 31 + kernel/bpf/syscall.c| 16 + 4 files changed, 165 insertions(+) -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html