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Although the memory tag commands use a memory tag manager to handle
addresses, that only removes the top byte.
That top byte is 4 bits of memory tag and 4 free bits, which is more
than it should strictly remove but that's how it is for now.
There are other non-address bit uses like pointer authentication.
To ensure the memory tag manager only has to deal with memory tags,
use the ABI plugin to remove the rest.
The tag access test has been updated to sign all the relevant pointers
and require that we're running on a system with pointer authentication
in addition to memory tagging.
The pointers will look like:
<4 bit user tag><4 bit memory tag><signature><bit virtual address>
Note that there is currently no API for reading memory tags. It will
also have to consider this when it arrives.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D117672
Files:
lldb/source/Commands/CommandObjectMemoryTag.cpp
lldb/test/API/linux/aarch64/mte_tag_access/TestAArch64LinuxMTEMemoryTagAccess.py
lldb/test/API/linux/aarch64/mte_tag_access/main.c
Index: lldb/test/API/linux/aarch64/mte_tag_access/main.c
===================================================================
--- lldb/test/API/linux/aarch64/mte_tag_access/main.c
+++ lldb/test/API/linux/aarch64/mte_tag_access/main.c
@@ -71,8 +71,9 @@
// tag
char *mte_buf_alt_tag = __arm_mte_create_random_tag(mte_buf, ~(1 << 10));
- // lldb should be removing the whole top byte, not just the tags.
- // So fill 63-60 with something non zero so we'll fail if we only remove tags.
+ // The memory tag manager should be removing the whole top byte, not just the
+ // tags. So fill 63-60 with something non zero so we'll fail if we only remove
+ // tags.
#define SET_TOP_NIBBLE(ptr, value) \
(char *)((size_t)(ptr) | ((size_t)((value)&0xf) << 60))
// mte_buf_alt_tag's nibble > mte_buf to check that lldb isn't just removing
@@ -82,6 +83,15 @@
mte_buf_2 = SET_TOP_NIBBLE(mte_buf_2, 0xC);
mte_read_only = SET_TOP_NIBBLE(mte_read_only, 0xD);
+// The top level commands should be removing all non-address bits, including
+// pointer signatures. This signs ptr with PAC key A. That signature goes
+// in some bits other than the top byte.
+#define sign_ptr(ptr) __asm__ __volatile__("pacdza %0" : "=r"(ptr) : "r"(ptr))
+ sign_ptr(mte_buf);
+ sign_ptr(mte_buf_alt_tag);
+ sign_ptr(mte_buf_2);
+ sign_ptr(mte_read_only);
+
// Breakpoint here
return 0;
}
Index: lldb/test/API/linux/aarch64/mte_tag_access/TestAArch64LinuxMTEMemoryTagAccess.py
===================================================================
--- lldb/test/API/linux/aarch64/mte_tag_access/TestAArch64LinuxMTEMemoryTagAccess.py
+++ lldb/test/API/linux/aarch64/mte_tag_access/TestAArch64LinuxMTEMemoryTagAccess.py
@@ -20,6 +20,11 @@
if not self.isAArch64MTE():
self.skipTest('Target must support MTE.')
+ # Required to check that commands remove non-address bits
+ # other than the memory tags.
+ if not self.isAArch64PAuth():
+ self.skipTest('Target must support pointer authentication')
+
self.build()
self.runCmd("file " + self.getBuildArtifact("a.out"), CURRENT_EXECUTABLE_SET)
Index: lldb/source/Commands/CommandObjectMemoryTag.cpp
===================================================================
--- lldb/source/Commands/CommandObjectMemoryTag.cpp
+++ lldb/source/Commands/CommandObjectMemoryTag.cpp
@@ -12,6 +12,7 @@
#include "lldb/Interpreter/OptionArgParser.h"
#include "lldb/Interpreter/OptionGroupFormat.h"
#include "lldb/Interpreter/OptionValueString.h"
+#include "lldb/Target/ABI.h"
#include "lldb/Target/Process.h"
using namespace lldb;
@@ -85,6 +86,17 @@
// If this fails the list of regions is cleared, so we don't need to read
// the return status here.
process->GetMemoryRegions(memory_regions);
+
+ lldb::addr_t logical_tag = tag_manager->GetLogicalTag(start_addr);
+
+ // The tag manager only removes tag bits. These addresses may include other
+ // non-address bits that must also be ignored.
+ ABISP abi = process->GetABI();
+ if (abi) {
+ start_addr = abi->FixDataAddress(start_addr);
+ end_addr = abi->FixDataAddress(end_addr);
+ }
+
llvm::Expected<MemoryTagManager::TagRange> tagged_range =
tag_manager->MakeTaggedRange(start_addr, end_addr, memory_regions);
@@ -101,7 +113,6 @@
return false;
}
- lldb::addr_t logical_tag = tag_manager->GetLogicalTag(start_addr);
result.AppendMessageWithFormatv("Logical tag: {0:x}", logical_tag);
result.AppendMessage("Allocation tags:");
@@ -231,6 +242,12 @@
// the return status here.
process->GetMemoryRegions(memory_regions);
+ // The tag manager only removes tag bits. These addresses may include other
+ // non-address bits that must also be ignored.
+ ABISP abi = process->GetABI();
+ if (abi)
+ start_addr = abi->FixDataAddress(start_addr);
+
// We have to assume start_addr is not granule aligned.
// So if we simply made a range:
// (start_addr, start_addr + (N * granule_size))
@@ -254,6 +271,10 @@
end_addr =
aligned_start_addr + (tags.size() * tag_manager->GetGranuleSize());
+ // Remove non-address bits that aren't memory tags
+ if (abi)
+ end_addr = abi->FixDataAddress(end_addr);
+
// Now we've aligned the start address so if we ask for another range
// using the number of tags N, we'll get back a range that is also N
// granules in size.
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