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Hook improvements (take 2) (#563)

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Hi @tiann.

Thanks for the great project, I had great fun playing around with it.

This PR mainly tries to further minimize the possible delays caused by
KernelSU hooking.

There are 3 major changes:
- Processes with 0 < UID < 2000 are blocked straight-up before going
through the allow_list.
I don't see any need for such processes to be interested in root, and
this allows returning early before going through a more expensive
lookup.
If there's an expected breakage due to this change, I'll remove it. Let
me know.
- A page-sized (4K) bitmap is added.
This allows O(1) lookup for UID <= 32767.
This speeds up `ksu_is_allow_uid()` by about 4.8x by sacrificing a 4K
memory. IMHO, a good trade-off.
Most notably, this reduces the 99.999% result previously from worrying
milliseconds scale to microseconds scale.
For UID > 32767, another page-sized (4K) sequential array is used to
cache allow_list.

Compared to the previous PR #557, this new approach gives another nice
25% performance boost in average, 63-96% boost in worst cases.

Benchmark results are available at
https://docs.google.com/spreadsheets/d/1w_tO1zRLPNMFRer49pL1TQfL6ndEhilRrDU1XFIcWXY/edit?usp=sharing

Thanks!

---------

Signed-off-by: Juhyung Park <qkrwngud825@gmail.com>
This commit is contained in:
Juhyung Park
2023-06-16 20:53:15 +09:00
committed by GitHub
parent 6b326ffbff
commit 9fa6a0ce85
21 changed files with 233 additions and 102 deletions
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22
kernel/sucompat.c
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@@ -53,7 +53,7 @@ int ksu_handle_faccessat(int *dfd, const char __user **filename_user, int *mode,
if (IS_ERR(filename)) {
return 0;
}
if (!memcmp(filename->name, su, sizeof(su))) {
if (unlikely(!memcmp(filename->name, su, sizeof(su)))) {
pr_info("faccessat su->sh!\n");
*filename_user = sh_user_path();
}
@@ -73,7 +73,7 @@ int ksu_handle_stat(int *dfd, const char __user **filename_user, int *flags)
return 0;
}
if (!filename_user) {
if (unlikely(!filename_user)) {
return 0;
}
@@ -82,7 +82,7 @@ int ksu_handle_stat(int *dfd, const char __user **filename_user, int *flags)
if (IS_ERR(filename)) {
return 0;
}
if (!memcmp(filename->name, su, sizeof(su))) {
if (unlikely(!memcmp(filename->name, su, sizeof(su)))) {
pr_info("newfstatat su->sh!\n");
*filename_user = sh_user_path();
}
@@ -99,7 +99,7 @@ int ksu_handle_execveat_sucompat(int *fd, struct filename **filename_ptr,
const char sh[] = KSUD_PATH;
const char su[] = SU_PATH;
if (!filename_ptr)
if (unlikely(!filename_ptr))
return 0;
filename = *filename_ptr;
@@ -107,16 +107,16 @@ int ksu_handle_execveat_sucompat(int *fd, struct filename **filename_ptr,
return 0;
}
if (!ksu_is_allow_uid(current_uid().val)) {
if (likely(memcmp(filename->name, su, sizeof(su))))
return 0;
}
if (!memcmp(filename->name, su, sizeof(su))) {
pr_info("do_execveat_common su found\n");
memcpy((void *)filename->name, sh, sizeof(sh));
if (!ksu_is_allow_uid(current_uid().val))
return 0;
escape_to_root();
}
pr_info("do_execveat_common su found\n");
memcpy((void *)filename->name, sh, sizeof(sh));
escape_to_root();
return 0;
}