[054/192] fs/proc/kcore: drop KCORE_REMAP and KCORE_OTHER

Commit Message

Andrew Morton July 1, 2021, 1:50 a.m. UTC

From: David Hildenbrand <[e-mail]>
Subject: fs/proc/kcore: drop KCORE_REMAP and KCORE_OTHER

Patch series "fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages", v3.

Looking for places where the kernel might unconditionally read
PageOffline() pages, I stumbled over /proc/kcore; turns out /proc/kcore
needs some more love to not touch some other pages we really don't want to
read -- i.e., hwpoisoned ones.

Examples for PageOffline() pages are pages inflated in a balloon, memory
unplugged via virtio-mem, and partially-present sections in memory added
by the Hyper-V balloon.

When reading pages inflated in a balloon, we essentially produce
unnecessary load in the hypervisor; holes in partially present sections in
case of Hyper-V are not accessible and already were a problem for
/proc/vmcore, fixed in makedumpfile by detecting PageOffline() pages.  In
the future, virtio-mem might disallow reading unplugged memory -- marked
as PageOffline() -- in some environments, resulting in undefined behavior
when accessed; therefore, I'm trying to identify and rework all these
(corner) cases.

With this series, there is really only access via /dev/mem, /proc/vmcore
and kdb left after I ripped out /dev/kmem.  kdb is an advanced corner-case
use case -- we won't care for now if someone explicitly tries to do nasty
things by reading from/writing to physical addresses we better not touch. 
/dev/mem is a use case we won't support for virtio-mem, at least for now,
so we'll simply disallow mapping any virtio-mem memory via /dev/mem next. 
/proc/vmcore is really only a problem when dumping the old kernel via
something that's not makedumpfile (read: basically never), however, we'll
try sanitizing that as well in the second kernel in the future.

Tested via kcore_dump:
	https://github.com/schlafwandler/kcore_dump
	


This patch (of 6):

Commit db779ef67ffe ("proc/kcore: Remove unused kclist_add_remap()")
removed the last user of KCORE_REMAP.

Commit 595dd46ebfc1 ("vfs/proc/kcore, x86/mm/kcore: Fix SMAP fault when
dumping vsyscall user page") removed the last user of KCORE_OTHER.

Let's drop both types.  While at it, also drop vaddr in "struct
kcore_list", used by KCORE_REMAP only.

Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: David Hildenbrand <[e-mail]>
Reviewed-by: Mike Rapoport <[e-mail]>
Cc: "Michael S. Tsirkin" <[e-mail]>
Cc: Jason Wang <[e-mail]>
Cc: Alexey Dobriyan <[e-mail]>
Cc: "Matthew Wilcox (Oracle)" <[e-mail]>
Cc: Oscar Salvador <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Alex Shi <[e-mail]>
Cc: Steven Price <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Cc: Aili Yao <[e-mail]>
Cc: Jiri Bohac <[e-mail]>
Cc: "K. Y. Srinivasan" <[e-mail]>
Cc: Haiyang Zhang <[e-mail]>
Cc: Stephen Hemminger <[e-mail]>
Cc: Wei Liu <[e-mail]>
Cc: Naoya Horiguchi <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 fs/proc/kcore.c       |    7 ++-----
 include/linux/kcore.h |    3 ---
 2 files changed, 2 insertions(+), 8 deletions(-)

Patch

--- a/fs/proc/kcore.c~fs-proc-kcore-drop-kcore_remap-and-kcore_other
+++ a/fs/proc/kcore.c
@@ -380,11 +380,8 @@  read_kcore(struct file *file, char __use
 			phdr->p_type = PT_LOAD;
 			phdr->p_flags = PF_R | PF_W | PF_X;
 			phdr->p_offset = kc_vaddr_to_offset(m->addr) + data_offset;
-			if (m->type == KCORE_REMAP)
-				phdr->p_vaddr = (size_t)m->vaddr;
-			else
-				phdr->p_vaddr = (size_t)m->addr;
-			if (m->type == KCORE_RAM || m->type == KCORE_REMAP)
+			phdr->p_vaddr = (size_t)m->addr;
+			if (m->type == KCORE_RAM)
 				phdr->p_paddr = __pa(m->addr);
 			else if (m->type == KCORE_TEXT)
 				phdr->p_paddr = __pa_symbol(m->addr);
--- a/include/linux/kcore.h~fs-proc-kcore-drop-kcore_remap-and-kcore_other
+++ a/include/linux/kcore.h
@@ -11,14 +11,11 @@  enum kcore_type {
 	KCORE_RAM,
 	KCORE_VMEMMAP,
 	KCORE_USER,
-	KCORE_OTHER,
-	KCORE_REMAP,
 };
 
 struct kcore_list {
 	struct list_head list;
 	unsigned long addr;
-	unsigned long vaddr;
 	size_t size;
 	int type;
 };