[PATCH v2] mm: hwpoison: coredump: support recovery from dump_user_range()

From: Kefeng Wang
Date: Mon Apr 17 2023 - 00:35:22 EST

The dump_user_range() is used to copy the user page to a coredump file,
but if a hardware memory error occurred during copy, which called from
__kernel_write_iter() in dump_user_range(), it crashes,

CPU: 112 PID: 7014 Comm: mca-recover Not tainted 6.3.0-rc2 #425

pc : __memcpy+0x110/0x260
lr : _copy_from_iter+0x3bc/0x4c8
...
Call trace:
__memcpy+0x110/0x260
copy_page_from_iter+0xcc/0x130
pipe_write+0x164/0x6d8
__kernel_write_iter+0x9c/0x210
dump_user_range+0xc8/0x1d8
elf_core_dump+0x308/0x368
do_coredump+0x2e8/0xa40
get_signal+0x59c/0x788
do_signal+0x118/0x1f8
do_notify_resume+0xf0/0x280
el0_da+0x130/0x138
el0t_64_sync_handler+0x68/0xc0
el0t_64_sync+0x188/0x190

Generally, the '->write_iter' of file ops will use copy_page_from_iter()
and copy_page_from_iter_atomic(), change memcpy() to copy_mc_to_kernel()
in both of them to handle #MC during source read, which stop coredump
processing and kill the task instead of kernel panic, but the source
address may not always a user address, so introduce a new copy_mc flag in
struct iov_iter{} to indicate that the iter could do a safe memory copy,
also introduce the helpers to set/cleck the flag, for now, it's only
used in coredump's dump_user_range(), but it could expand to any other
scenarios to fix the similar issue.

Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Tong Tiangen <tongtiangen@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
v2:
- move the helper functions under pre-existing CONFIG_ARCH_HAS_COPY_MC
- reposition the copy_mc in struct iov_iter for easy merge, suggested
by Andrew Morton
- drop unnecessary clear flag helper
- fix checkpatch warning
fs/coredump.c | 1 +
include/linux/uio.h | 16 ++++++++++++++++
lib/iov_iter.c | 17 +++++++++++++++--
3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 5df1e6e1eb2b..ece7badf701b 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -882,6 +882,7 @@ static int dump_emit_page(struct coredump_params *cprm, struct page *page)
pos = file->f_pos;
bvec_set_page(&bvec, page, PAGE_SIZE, 0);
iov_iter_bvec(&iter, ITER_SOURCE, &bvec, 1, PAGE_SIZE);
+ iov_iter_set_copy_mc(&iter);
n = __kernel_write_iter(cprm->file, &iter, &pos);
if (n != PAGE_SIZE)
return 0;
diff --git a/include/linux/uio.h b/include/linux/uio.h
index c459e1d5772b..aa3a4c6ba585 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -40,6 +40,7 @@ struct iov_iter_state {

struct iov_iter {
u8 iter_type;
+ bool copy_mc;
bool nofault;
bool data_source;
bool user_backed;
@@ -241,8 +242,22 @@ size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i);

#ifdef CONFIG_ARCH_HAS_COPY_MC
size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
+static inline void iov_iter_set_copy_mc(struct iov_iter *i)
+{
+ i->copy_mc = true;
+}
+
+static inline bool iov_iter_is_copy_mc(const struct iov_iter *i)
+{
+ return i->copy_mc;
+}
#else
#define _copy_mc_to_iter _copy_to_iter
+static inline void iov_iter_set_copy_mc(struct iov_iter *i) { }
+static inline bool iov_iter_is_copy_mc(const struct iov_iter *i)
+{
+ return false;
+}
#endif

size_t iov_iter_zero(size_t bytes, struct iov_iter *);
@@ -357,6 +372,7 @@ static inline void iov_iter_ubuf(struct iov_iter *i, unsigned int direction,
WARN_ON(direction & ~(READ | WRITE));
*i = (struct iov_iter) {
.iter_type = ITER_UBUF,
+ .copy_mc = false,
.user_backed = true,
.data_source = direction,
.ubuf = buf,
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 08587feb94cc..7b9d8419fee7 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -288,6 +288,7 @@ void iov_iter_init(struct iov_iter *i, unsigned int direction,
WARN_ON(direction & ~(READ | WRITE));
*i = (struct iov_iter) {
.iter_type = ITER_IOVEC,
+ .copy_mc = false,
.nofault = false,
.user_backed = true,
.data_source = direction,
@@ -371,6 +372,14 @@ size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
EXPORT_SYMBOL_GPL(_copy_mc_to_iter);
#endif /* CONFIG_ARCH_HAS_COPY_MC */

+static void *memcpy_from_iter(struct iov_iter *i, void *to, const void *from,
+ size_t size)
+{
+ if (iov_iter_is_copy_mc(i))
+ return (void *)copy_mc_to_kernel(to, from, size);
+ return memcpy(to, from, size);
+}
+
size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
{
if (WARN_ON_ONCE(!i->data_source))
@@ -380,7 +389,7 @@ size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
might_fault();
iterate_and_advance(i, bytes, base, len, off,
copyin(addr + off, base, len),
- memcpy(addr + off, base, len)
+ memcpy_from_iter(i, addr + off, base, len)
)

return bytes;
@@ -571,7 +580,7 @@ size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, size_t byt
}
iterate_and_advance(i, bytes, base, len, off,
copyin(p + off, base, len),
- memcpy(p + off, base, len)
+ memcpy_from_iter(i, p + off, base, len)
)
kunmap_atomic(kaddr);
return bytes;
@@ -704,6 +713,7 @@ void iov_iter_kvec(struct iov_iter *i, unsigned int direction,
WARN_ON(direction & ~(READ | WRITE));
*i = (struct iov_iter){
.iter_type = ITER_KVEC,
+ .copy_mc = false,
.data_source = direction,
.kvec = kvec,
.nr_segs = nr_segs,
@@ -720,6 +730,7 @@ void iov_iter_bvec(struct iov_iter *i, unsigned int direction,
WARN_ON(direction & ~(READ | WRITE));
*i = (struct iov_iter){
.iter_type = ITER_BVEC,
+ .copy_mc = false,
.data_source = direction,
.bvec = bvec,
.nr_segs = nr_segs,
@@ -748,6 +759,7 @@ void iov_iter_xarray(struct iov_iter *i, unsigned int direction,
BUG_ON(direction & ~1);
*i = (struct iov_iter) {
.iter_type = ITER_XARRAY,
+ .copy_mc = false,
.data_source = direction,
.xarray = xarray,
.xarray_start = start,
@@ -771,6 +783,7 @@ void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count)
BUG_ON(direction != READ);
*i = (struct iov_iter){
.iter_type = ITER_DISCARD,
+ .copy_mc = false,
.data_source = false,
.count = count,
.iov_offset = 0
--
2.35.3