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authorLinus Torvalds <torvalds@linux-foundation.org>2015-04-07 10:33:49 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-04-08 14:35:48 -0700
commit3afe9f849600645723246baa95e7559caeca6ce9 (patch)
tree6de4adcc568a7df591f3b73f36ecb8736eb9168d
parentcae2a173fe94ab3a437416af6f092fae2e65837e (diff)
downloadlinux-3afe9f849600645723246baa95e7559caeca6ce9.tar.bz2
Copy the kernel module data from user space in chunks
Unlike most (all?) other copies from user space, kernel module loading is almost unlimited in size. So we do a potentially huge "copy_from_user()" when we copy the module data from user space to the kernel buffer, which can be a latency concern when preemption is disabled (or voluntary). Also, because 'copy_from_user()' clears the tail of the kernel buffer on failures, even a *failed* copy can end up wasting a lot of time. Normally neither of these are concerns in real life, but they do trigger when doing stress-testing with trinity. Running in a VM seems to add its own overheadm causing trinity module load testing to even trigger the watchdog. The simple fix is to just chunk up the module loading, so that it never tries to copy insanely big areas in one go. That bounds the latency, and also the amount of (unnecessarily, in this case) cleared memory for the failure case. Reported-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--kernel/module.c19
1 files changed, 18 insertions, 1 deletions
diff --git a/kernel/module.c b/kernel/module.c
index 99fdf94efce8..ec53f594e9c9 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2479,6 +2479,23 @@ static int elf_header_check(struct load_info *info)
return 0;
}
+#define COPY_CHUNK_SIZE (16*PAGE_SIZE)
+
+static int copy_chunked_from_user(void *dst, const void __user *usrc, unsigned long len)
+{
+ do {
+ unsigned long n = min(len, COPY_CHUNK_SIZE);
+
+ if (copy_from_user(dst, usrc, n) != 0)
+ return -EFAULT;
+ cond_resched();
+ dst += n;
+ usrc += n;
+ len -= n;
+ } while (len);
+ return 0;
+}
+
/* Sets info->hdr and info->len. */
static int copy_module_from_user(const void __user *umod, unsigned long len,
struct load_info *info)
@@ -2498,7 +2515,7 @@ static int copy_module_from_user(const void __user *umod, unsigned long len,
if (!info->hdr)
return -ENOMEM;
- if (copy_from_user(info->hdr, umod, info->len) != 0) {
+ if (copy_chunked_from_user(info->hdr, umod, info->len) != 0) {
vfree(info->hdr);
return -EFAULT;
}