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mm/madvise: unrestrict process_madvise() for current process

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The process_madvise() call was introduced in commit ecb8ac8b1f
("mm/madvise: introduce process_madvise() syscall: an external memory
hinting API") as a means of performing madvise() operations on another
process.

However, as it provides the means by which to perform multiple madvise()
operations in a batch via an iovec, it is useful to utilise the same
interface for performing operations on the current process rather than a
remote one.

Commit 22af8caff7 ("mm/madvise: process_madvise() drop capability check
if same mm") removed the need for a caller invoking process_madvise() on
its own pidfd to possess the CAP_SYS_NICE capability, however this leaves
the restrictions on operation in place.

Resolve this by only applying the restriction on operations when accessing
a remote process.

Moving forward we plan to implement a simpler means of specifying this
condition other than needing to establish a self pidfd, perhaps in the
form of a sentinel pidfd.

Also take the opportunity to refactor the system call implementation
abstracting the vectorised operation.

Link: https://lkml.kernel.org/r/20240926151019.82902-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christian Brauner <brauner@kernel.org>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lorenzo Stoakes 2024-09-26 16:10:19 +01:00 committed by Andrew Morton
parent f33cea94e3
commit 021781b012
1 changed files with 36 additions and 19 deletions
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55
mm/madvise.c
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@ -1208,7 +1208,8 @@ madvise_behavior_valid(int behavior)
}
}
static bool process_madvise_behavior_valid(int behavior)
/* Can we invoke process_madvise() on a remote mm for the specified behavior? */
static bool process_madvise_remote_valid(int behavior)
{
switch (behavior) {
case MADV_COLD:
@ -1477,6 +1478,28 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
return do_madvise(current->mm, start, len_in, behavior);
}
/* Perform an madvise operation over a vector of addresses and lengths. */
static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
int behavior)
{
ssize_t ret = 0;
size_t total_len;
total_len = iov_iter_count(iter);
while (iov_iter_count(iter)) {
ret = do_madvise(mm, (unsigned long)iter_iov_addr(iter),
iter_iov_len(iter), behavior);
if (ret < 0)
break;
iov_iter_advance(iter, iter_iov_len(iter));
}
ret = (total_len - iov_iter_count(iter)) ? : ret;
return ret;
}
SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
size_t, vlen, int, behavior, unsigned int, flags)
{
@ -1486,7 +1509,6 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
struct iov_iter iter;
struct task_struct *task;
struct mm_struct *mm;
size_t total_len;
unsigned int f_flags;
if (flags != 0) {
@ -1504,11 +1526,6 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
goto free_iov;
}
if (!process_madvise_behavior_valid(behavior)) {
ret = -EINVAL;
goto release_task;
}
/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */
mm = mm_access(task, PTRACE_MODE_READ_FSCREDS);
if (IS_ERR(mm)) {
@ -1516,26 +1533,26 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
goto release_task;
}
/*
* We need only perform this check if we are attempting to manipulate a
* remote process's address space.
*/
if (mm != current->mm && !process_madvise_remote_valid(behavior)) {
ret = -EINVAL;
goto release_mm;
}
/*
* Require CAP_SYS_NICE for influencing process performance. Note that
* only non-destructive hints are currently supported.
* only non-destructive hints are currently supported for remote
* processes.
*/
if (mm != current->mm && !capable(CAP_SYS_NICE)) {
ret = -EPERM;
goto release_mm;
}
total_len = iov_iter_count(&iter);
while (iov_iter_count(&iter)) {
ret = do_madvise(mm, (unsigned long)iter_iov_addr(&iter),
iter_iov_len(&iter), behavior);
if (ret < 0)
break;
iov_iter_advance(&iter, iter_iov_len(&iter));
}
ret = (total_len - iov_iter_count(&iter)) ? : ret;
ret = vector_madvise(mm, &iter, behavior);
release_mm:
mmput(mm);