[PATCHv3 16/27] x86/vdso: Switch image on setns()/unshare()/clone()
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STALE2731d
SUPERSEDED
From: Dmitry Safonov <hidden>
Date: 2019-04-25 16:14:51
Also in:
lkml
Subsystem:
the rest, x86 architecture (32-bit and 64-bit), x86 entry code, x86 vdso · Maintainers:
Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, Andy Lutomirski
Revision v3 of 7 in this series.
Revisions (7)
As it has been discussed on timens RFC, adding a new conditional branch `if (inside_time_ns)` on VDSO for all processes is undesirable. It will add a penalty for everybody as branch predictor may mispredict the jump. Also there are instruction cache lines wasted on cmp/jmp. Those effects of introducing time namespace are very much unwanted having in mind how much work have been spent on micro-optimisation vdso code. Addressing those problems, there are two versions of VDSO's .so: for host tasks (without any penalty) and for processes inside of time namespace with clk_to_ns() that subtracts offsets from host's time. Whenever a user does setns()/unshare() or clone() with CLONE_TIMENS, change VDSO image in mm and zap existing VVAR/VDSO page tables. They will be re-faulted with corresponding image and VVAR offsets. Co-developed-by: Andrei Vagin <redacted> Signed-off-by: Andrei Vagin <redacted> Signed-off-by: Dmitry Safonov <redacted> --- arch/x86/entry/vdso/vma.c | 29 +++++++++++++++++++++++++++++ arch/x86/include/asm/vdso.h | 1 + kernel/time_namespace.c | 11 +++++++++++ 3 files changed, 41 insertions(+)
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 6aae9c0d400d..28628950214d 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c@@ -25,6 +25,7 @@ #include <asm/cpufeature.h> #include <asm/mshyperv.h> #include <asm/page.h> +#include <asm/tlb.h> #if defined(CONFIG_X86_64) unsigned int __read_mostly vdso64_enabled = 1;
@@ -189,6 +190,34 @@ static const struct vm_special_mapping vvar_mapping = { .mremap = vvar_mremap, }; +#ifdef CONFIG_TIME_NS +int vdso_join_timens(struct task_struct *task, bool inside_ns) +{ + struct mm_struct *mm = task->mm; + struct vm_area_struct *vma; + + if (down_write_killable(&mm->mmap_sem)) + return -EINTR; + + for (vma = mm->mmap; vma; vma = vma->vm_next) { + unsigned long size = vma->vm_end - vma->vm_start; + + if (vma_is_special_mapping(vma, &vvar_mapping)) + zap_page_range(vma, vma->vm_start, size); + if (vma_is_special_mapping(vma, &vdso_mapping)) + zap_page_range(vma, vma->vm_start, size); + } + + up_write(&mm->mmap_sem); + return 0; +} +#else /* CONFIG_TIME_NS */ +int vdso_join_timens(struct task_struct *task, bool inside_ns) +{ + return -ENXIO; +} +#endif + /* * Add vdso and vvar mappings to current process. * @image - blob to map
diff --git a/arch/x86/include/asm/vdso.h b/arch/x86/include/asm/vdso.h
index a620c7f23425..583133446874 100644
--- a/arch/x86/include/asm/vdso.h
+++ b/arch/x86/include/asm/vdso.h@@ -46,6 +46,7 @@ extern struct vdso_image vdso_image_32; extern void __init init_vdso_image(struct vdso_image *image); extern int map_vdso_once(const struct vdso_image *image, unsigned long addr); +extern int vdso_join_timens(struct task_struct *task, bool inside_ns); #endif /* __ASSEMBLER__ */
diff --git a/kernel/time_namespace.c b/kernel/time_namespace.c
index 4828447721ec..e806accc4eaf 100644
--- a/kernel/time_namespace.c
+++ b/kernel/time_namespace.c@@ -14,6 +14,7 @@ #include <linux/proc_ns.h> #include <linux/sched/task.h> #include <linux/mm.h> +#include <asm/vdso.h> static struct ucounts *inc_time_namespaces(struct user_namespace *ns) {
@@ -155,11 +156,16 @@ static void timens_put(struct ns_common *ns) static int timens_install(struct nsproxy *nsproxy, struct ns_common *new) { struct time_namespace *ns = to_time_ns(new); + int ret; if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) || !ns_capable(current_user_ns(), CAP_SYS_ADMIN)) return -EPERM; + ret = vdso_join_timens(current, ns != &init_time_ns); + if (ret) + return ret; + get_time_ns(ns); get_time_ns(ns); put_time_ns(nsproxy->time_ns);
@@ -174,10 +180,15 @@ int timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk) { struct ns_common *nsc = &nsproxy->time_ns_for_children->ns; struct time_namespace *ns = to_time_ns(nsc); + int ret; if (nsproxy->time_ns == nsproxy->time_ns_for_children) return 0; + ret = vdso_join_timens(tsk, ns != &init_time_ns); + if (ret) + return ret; + get_time_ns(ns); put_time_ns(nsproxy->time_ns); nsproxy->time_ns = ns;
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2.21.0