fix(mm): fix brk syscall to properly map heap pages #92
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The original brk implementation had several issues: 1. Never actually mapped pages - only updated the heap_top pointer 2. Limit was USER_HEAP_SIZE (64KB), too small for real programs 3. Did not track initial heap region, causing double-mapping errors Changes: - Actually call aspace.map() to map new heap pages on expansion - Increase limit to USER_HEAP_SIZE_MAX (512MB) - Track initial_heap_end to avoid re-mapping already mapped pages - Add USER_HEAP_SIZE_MAX config for all architectures
guoweikang
reviewed
Dec 19, 2025
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| /// The address of signal trampoline. | ||
| pub const SIGNAL_TRAMPOLINE: usize = 0x4001_0000; | ||
| pub const SIGNAL_TRAMPOLINE: usize = USER_STACK_TOP - USER_STACK_SIZE - 0x1000; |
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--------------- user-space(end) : 0x7fff_ffff_f000
--------------- stack-top： 0x7fff_0000_0000
STACK SPACE （size: 0x8_0000）
-------------- stack-end： 0x7fff_0000_0000 - 0x8_0000
SIGNAL TRAP
--------------- SIGNAL TRAP
If we put SIGNAL_TRAMPOLINE under stack, if stack overaccess happend, it wouldn't directly give us an error(invalid Virtual Address), it can overwrite(read) SIGNAL_TRAMPOLINE mem!
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we should put SINGAL TRAP on stack limit above
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The original brk implementation had several issues:
Implementation
File:
api/src/syscall/mm/brk.rsBug Description:
The original
brkimplementation did not properly track the initial heap region that was already mapped during ELF loading. When a process calledbrkto expand the heap, it would attempt to map pages that were already mapped, causingAlreadyExistserrors.Fix:
initial_heap_end(USER_HEAP_BASE + USER_HEAP_SIZE) as the end of the pre-mapped regioninitial_heap_end.max(current_top_aligned)as the expansion start pointsaturating_subto avoid negative sizesFiles:
core/src/config/aarch64.rscore/src/config/loongarch64.rscore/src/config/riscv64.rscore/src/config/x86_64.rsDescription:
Added
USER_HEAP_SIZE_MAX(512MB) constant to limit maximum heap expansion viabrk. This prevents unlimited heap growth.