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JitArm64: Make HandleFastmemFault less unsafe 

HandleFastmemFault works correctly when faults only happen in
expected locations, but it does some things that are rather
dangerous for faults in unexpected locations, like decrementing
an iterator without checking whether it's equal to begin.

This change cleans up the logic by making m_fault_to_handler's
key be the end of the fastmem region instead of the start.
This commit is contained in:
JosJuice 2021-08-22 19:51:21 +02:00
parent 33154de614
commit 0cf8405126
2 changed files with 12 additions and 13 deletions
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2
Source/Core/Core/PowerPC/JitArm64/Jit.h
View File

@ -195,7 +195,7 @@ protected:
struct FastmemArea struct FastmemArea
{ {
u32 length; const u8* fastmem_code;
const u8* slowmem_code; const u8* slowmem_code;
}; };

23
Source/Core/Core/PowerPC/JitArm64/JitArm64_BackPatch.cpp
View File

@ -134,7 +134,7 @@ void JitArm64::EmitBackpatchRoutine(u32 flags, bool fastmem, bool do_farcode, AR
handler.fprs = fprs_to_push; handler.fprs = fprs_to_push;
handler.flags = flags; handler.flags = flags;
FastmemArea* fastmem_area = &m_fault_to_handler[fastmem_start]; FastmemArea* fastmem_area = &m_fault_to_handler[fastmem_end];
auto handler_loc_iter = m_handler_to_loc.find(handler); auto handler_loc_iter = m_handler_to_loc.find(handler);
if (handler_loc_iter == m_handler_to_loc.end()) if (handler_loc_iter == m_handler_to_loc.end())
@ -143,14 +143,14 @@ void JitArm64::EmitBackpatchRoutine(u32 flags, bool fastmem, bool do_farcode, AR
SwitchToFarCode(); SwitchToFarCode();
const u8* handler_loc = GetCodePtr(); const u8* handler_loc = GetCodePtr();
m_handler_to_loc[handler] = handler_loc; m_handler_to_loc[handler] = handler_loc;
fastmem_area->fastmem_code = fastmem_start;
fastmem_area->slowmem_code = handler_loc; fastmem_area->slowmem_code = handler_loc;
fastmem_area->length = fastmem_end - fastmem_start;
} }
else else
{ {
const u8* handler_loc = handler_loc_iter->second; const u8* handler_loc = handler_loc_iter->second;
fastmem_area->fastmem_code = fastmem_start;
fastmem_area->slowmem_code = handler_loc; fastmem_area->slowmem_code = handler_loc;
fastmem_area->length = fastmem_end - fastmem_start;
return; return;
} }
} }
@ -253,33 +253,32 @@ bool JitArm64::HandleFastmemFault(uintptr_t access_address, SContext* ctx)
return false; return false;
} }
auto slow_handler_iter = m_fault_to_handler.upper_bound((const u8*)ctx->CTX_PC); const u8* pc = reinterpret_cast<const u8*>(ctx->CTX_PC);
slow_handler_iter--; auto slow_handler_iter = m_fault_to_handler.upper_bound(pc);
// no fastmem area found // no fastmem area found
if (slow_handler_iter == m_fault_to_handler.end()) if (slow_handler_iter == m_fault_to_handler.end())
return false; return false;
const u8* fault_location = slow_handler_iter->first; const u8* fastmem_area_start = slow_handler_iter->second.fastmem_code;
const u32 fastmem_area_length = slow_handler_iter->second.length; const u8* fastmem_area_end = slow_handler_iter->first;
// no overlapping fastmem area found // no overlapping fastmem area found
if ((const u8*)ctx->CTX_PC - fault_location > fastmem_area_length) if (pc < fastmem_area_start)
return false; return false;
const Common::ScopedJITPageWriteAndNoExecute enable_jit_page_writes; const Common::ScopedJITPageWriteAndNoExecute enable_jit_page_writes;
ARM64XEmitter emitter((u8*)fault_location); ARM64XEmitter emitter(const_cast<u8*>(fastmem_area_start));
emitter.BL(slow_handler_iter->second.slowmem_code); emitter.BL(slow_handler_iter->second.slowmem_code);
const u32 num_insts_max = fastmem_area_length / 4 - 1; while (emitter.GetCodePtr() < fastmem_area_end)
for (u32 i = 0; i < num_insts_max; ++i)
emitter.NOP(); emitter.NOP();
m_fault_to_handler.erase(slow_handler_iter); m_fault_to_handler.erase(slow_handler_iter);
emitter.FlushIcache(); emitter.FlushIcache();
ctx->CTX_PC = reinterpret_cast<std::uintptr_t>(fault_location); ctx->CTX_PC = reinterpret_cast<std::uintptr_t>(fastmem_area_start);
return true; return true;
} }