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Kernel: Clear up some comments in the sys$mprotect implementation

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This commit is contained in:
Idan Horowitz 2021-12-01 19:29:08 +02:00
parent f27bbec7b2
commit d5d0eb45bf
Notes: sideshowbarker 2024-07-17 23:13:29 +09:00 
Author: https://github.com/IdanHo
Commit: https://github.com/SerenityOS/serenity/commit/d5d0eb45bf9
Pull-request: https://github.com/SerenityOS/serenity/pull/10674
Reviewed-by: https://github.com/bgianfo
Reviewed-by: https://github.com/linusg ✅
1 changed files with 6 additions and 4 deletions
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10
Kernel/Syscalls/mmap.cpp
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@ -325,7 +325,7 @@ ErrorOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int p
if (const auto& regions = address_space().find_regions_intersecting(range_to_mprotect); regions.size()) {
size_t full_size_found = 0;
// first check before doing anything
// Check that all intersecting regions are compatible.
for (const auto* region : regions) {
if (!region->is_mmap())
return EPERM;
@ -341,13 +341,14 @@ ErrorOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int p
if (full_size_found != range_to_mprotect.size())
return ENOMEM;
// then do all the other stuff
// Finally, iterate over each region, either updating its access flags if the range covers it wholly,
// or carving out a new subregion with the appropriate access flags set.
for (auto* old_region : regions) {
if (old_region->access() == Memory::prot_to_region_access_flags(prot))
continue;
const auto intersection_to_mprotect = range_to_mprotect.intersect(old_region->range());
// full sub region
// If the region is completely covered by range, simply update the access flags
if (intersection_to_mprotect == old_region->range()) {
old_region->set_readable(prot & PROT_READ);
old_region->set_writable(prot & PROT_WRITE);
@ -367,7 +368,8 @@ ErrorOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int p
// We need to allocate a new region for the range we wanted to change permission bits on.
auto adjacent_regions = TRY(address_space().try_split_region_around_range(*old_region, intersection_to_mprotect));
// there should only be one
// Since the range is not contained in a single region, it can only partially cover its starting and ending region,
// therefore carving out a chunk from the region will always produce a single extra region, and not two.
VERIFY(adjacent_regions.size() == 1);
size_t new_range_offset_in_vmobject = old_region->offset_in_vmobject() + (intersection_to_mprotect.base().get() - old_region->range().base().get());