Hi Greg et al. Many DRAM modules are susceptible to disturbance errors as outlined by Kim et al. in June of last year [1]. More recently, a methodology to exploit these memory cell interactions to escalate privileges on Linux was made public by Google's Project Zero [2].
One attack vector detailed in their methodology uses information gleaned from virtual page - frame maps. As a hardening/mitigation response, ab676b7d6fbf [3] restricts access to /proc/*/pagemap to privileged userspace. I noticed 3.14.37 was the only LT kernel to receive a backport of this mitigation. Attached please find a backport for use on 3.10.y (candidate for inclusion in 3.10.74). 3.12.y and 3.18.y can probably use [3] pretty much directly while 3.2.y and 3.4.y can likely use my patch with a little offset TLC. --mancha [1] http://users.ece.cmu.edu/~yoonguk/papers/kim-isca14.pdf [2] http://googleprojectzero.blogspot.com/2015/03/exploiting-dram-rowhammer-bug-to-gain.html [3] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ab676b7d6fbf
From e650025c3a4e86ef8accdb679ca3adbd4fdbf4fb Mon Sep 17 00:00:00 2001 From: mancha security <[email protected]> Date: Sat, 28 Mar 2015 19:11:29 +0000 Subject: [PATCH] pagemap: do not leak physical addresses to non-privileged userspace Backport of: commit ab676b7d6fbf4b294bf198fb27ade5b0e865c7ce Author: Kirill A. Shutemov <[email protected]> Date: Mon Mar 9 23:11:12 2015 +0200 As pointed by recent post[1] on exploiting DRAM physical imperfection, /proc/PID/pagemap exposes sensitive information which can be used to do attacks. This disallows anybody without CAP_SYS_ADMIN to read the pagemap. [1] http://googleprojectzero.blogspot.com/2015/03/exploiting-dram-rowhammer-bug-to-gain.html [ Eventually we might want to do anything more finegrained, but for now this is the simple model. - Linus ] Signed-off-by: Kirill A. Shutemov <[email protected]> Acked-by: Konstantin Khlebnikov <[email protected]> Acked-by: Andy Lutomirski <[email protected]> Cc: Pavel Emelyanov <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Mark Seaborn <[email protected]> Cc: [email protected] Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: mancha security <[email protected]> --- fs/proc/task_mmu.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 65fc60a..be9c7bb 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1110,9 +1110,19 @@ out: return ret; } +static int pagemap_open(struct inode *inode, struct file *file) +{ + /* do not disclose physical addresses to unprivileged + userspace (closes a rowhammer attack vector) */ + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; + return 0; +} + const struct file_operations proc_pagemap_operations = { .llseek = mem_lseek, /* borrow this */ .read = pagemap_read, + .open = pagemap_open, }; #endif /* CONFIG_PROC_PAGE_MONITOR */ -- 1.8.3.1
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