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Merge empty mappings within a library so they form a single contiguous range #89

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Merged
gabrielesvelto merged 1 commit into from
Sep 19, 2023
Merged

Merge empty mappings within a library so they form a single contiguous range #89

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105 changes: 84 additions & 21 deletions src/linux/maps_reader.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,14 @@ impl MappingInfo {
is_mapping_a_path(self.name.as_deref())
}

pub fn is_empty_page(&self) -> bool {
(self.offset == 0) && (self.permissions == MMPermissions::PRIVATE) && self.name.is_none()
}

pub fn end_address(&self) -> usize {
self.start_address + self.size
}

pub fn aggregate(memory_maps: MemoryMaps, linux_gate_loc: AuxvType) -> Result<Vec<Self>> {
let mut infos = Vec::<Self>::new();

Expand Down Expand Up @@ -99,31 +107,54 @@ impl MappingInfo {
offset = 0;
}

// Merge adjacent mappings into one module, assuming they're a single
// library mapped by the dynamic linker.
if let Some(module) = infos.last_mut() {
if pathname.is_some() {
if (start_address == module.start_address + module.size)
&& (pathname == module.name)
{
module.system_mapping_info.end_address = end_address;
module.size = end_address - module.start_address;
module.permissions |= mm.perms;
continue;
}
} else {
if let Some(prev_module) = infos.last_mut() {
if (start_address == prev_module.end_address())
&& pathname.is_some()
&& (pathname == prev_module.name)
{
// Merge adjacent mappings into one module, assuming they're a single
// library mapped by the dynamic linker.
prev_module.system_mapping_info.end_address = end_address;
prev_module.size = end_address - prev_module.start_address;
prev_module.permissions |= mm.perms;
continue;
} else if (start_address == prev_module.end_address())
&& prev_module.is_executable()
&& prev_module.name_is_path()
&& ((offset == 0) || (offset == prev_module.end_address()))
&& (mm.perms == MMPermissions::PRIVATE)
{
// Also merge mappings that result from address ranges that the
// linker reserved but which a loaded library did not use. These
// appear as an anonymous private mapping with no access flags set
// and which directly follow an executable mapping.
let module_end_address = module.start_address + module.size;
if (start_address == module_end_address)
&& module.is_executable()
&& is_mapping_a_path(module.name.as_deref())
&& (offset == 0 || offset == module_end_address)
&& mm.perms == MMPermissions::PRIVATE
{
module.size = end_address - module.start_address;
prev_module.size = end_address - prev_module.start_address;
continue;
}
}

// Sometimes the unused ranges reserved but the linker appear within the library.
// If we detect an empty page that is adjacent to two mappings of the same library
// we fold the three mappings together.
if let Some(previous_modules) = infos.rchunks_exact_mut(2).next() {
let empty_page = if let Some(prev_module) = previous_modules.last() {
let prev_prev_module = previous_modules.first().unwrap();
prev_prev_module.name_is_path()
&& (prev_prev_module.end_address() == prev_module.start_address)
&& prev_module.is_empty_page()
&& (prev_module.end_address() == start_address)
} else {
false
};

if empty_page {
let prev_prev_module = previous_modules.first_mut().unwrap();

if pathname == prev_prev_module.name {
prev_prev_module.system_mapping_info.end_address = end_address;
prev_prev_module.size = end_address - prev_prev_module.start_address;
prev_prev_module.permissions |= mm.perms;
infos.pop();
continue;
}
}
Expand Down Expand Up @@ -553,6 +584,38 @@ ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0 [vsysca
assert_eq!(mappings[6], gate_map);
}

#[test]
fn test_merged_reserved_mappings_within_module() {
let mappings = get_mappings_for(
"\
9b4a0000-9b931000 r--p 00000000 08:12 393449 /data/app/org.mozilla.firefox-1/lib/x86/libxul.so
9b931000-9bcae000 ---p 00000000 00:00 0
9bcae000-a116b000 r-xp 00490000 08:12 393449 /data/app/org.mozilla.firefox-1/lib/x86/libxul.so
a116b000-a4562000 r--p 0594d000 08:12 393449 /data/app/org.mozilla.firefox-1/lib/x86/libxul.so
a4562000-a4563000 ---p 00000000 00:00 0
a4563000-a4840000 r--p 08d44000 08:12 393449 /data/app/org.mozilla.firefox-1/lib/x86/libxul.so
a4840000-a4873000 rw-p 09021000 08:12 393449 /data/app/org.mozilla.firefox-1/lib/x86/libxul.so",
0xa4876000,
);

let gate_map = MappingInfo {
start_address: 0x9b4a0000,
size: 155004928, // Merged the anonymous area after in this mapping, so its bigger..
system_mapping_info: SystemMappingInfo {
start_address: 0x9b4a0000,
end_address: 0xa4873000,
},
offset: 0,
permissions: MMPermissions::READ
| MMPermissions::WRITE
| MMPermissions::EXECUTE
| MMPermissions::PRIVATE,
name: Some("/data/app/org.mozilla.firefox-1/lib/x86/libxul.so".into()),
};

assert_eq!(mappings[0], gate_map);
}

#[test]
fn test_get_mapping_effective_name() {
let mappings = get_mappings_for(
Expand Down