[Bug 1905356] [NEW] No check for unaligned data access in ARM32 instructions

[JIANG Muhui]

Public bug reported:

hi

According to the ARM documentation, there are alignment requirements of
load/store instructions.  Alignment fault should be raised if the
alignment check is failed. However, it seems that QEMU doesn't implement
this, which is against the documentation of ARM. For example, the
instruction LDRD/STRD/LDREX/STREX must check the address is word
alignment no matter what value the SCTLR.A is.

I attached a testcase, which contains an instruction at VA 0x10240: ldrd
r0,[pc.#1] in the main function. QEMU can successfully load the data in
the unaligned address. The test is done in QEMU 5.1.0. I can provide
more testcases for the other instructions if you need. Many thanks.

To patch this, we need a check while we translate the instruction to
tcg. If the address is unaligned, a signal number (i.e., SIGBUS) should
be raised.

Regards
Muhui

** Affects: qemu
     Importance: Undecided
         Status: New

** Attachment added: "case_ldrd_arm"
   
https://bugs.launchpad.net/bugs/1905356/+attachment/5437364/+files/case_ldrd_arm

** Description changed:

  hi
  
  According to the ARM documentation, there are alignment requirements of
  load/store instructions.  Alignment fault should be raised if the
  alignment check is failed. However, it seems that QEMU doesn't implement
  this, which is against the documentation of ARM. For example, the
  instruction LDRD/STRD/LDREX/STREX must check the address is word
  alignment no matter what value the SCTLR.A is.
  
- I attached a testcase, which contains a instruction at VA 0x10240: ldrd
+ I attached a testcase, which contains an instruction at VA 0x10240: ldrd
  r0,[pc.#1] in the main function. QEMU can successfully load the data in
  the unaligned address. The test is done in QEMU 5.1.0. I can provide
  more testcases for the other instructions if you need. Many thanks.
  
  To patch this, we need a check while we translate the instruction to
  tcg. If the address is unaligned, a signal number (i.e., SIGBUS) should
  be raised.
  
  Regards
  Muhui

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https://bugs.launchpad.net/bugs/1905356

Title:
  No check for unaligned data access in ARM32 instructions

Status in QEMU:
  New

Bug description:
  hi

  According to the ARM documentation, there are alignment requirements
  of load/store instructions.  Alignment fault should be raised if the
  alignment check is failed. However, it seems that QEMU doesn't
  implement this, which is against the documentation of ARM. For
  example, the instruction LDRD/STRD/LDREX/STREX must check the address
  is word alignment no matter what value the SCTLR.A is.

  I attached a testcase, which contains an instruction at VA 0x10240:
  ldrd r0,[pc.#1] in the main function. QEMU can successfully load the
  data in the unaligned address. The test is done in QEMU 5.1.0. I can
  provide more testcases for the other instructions if you need. Many
  thanks.

  To patch this, we need a check while we translate the instruction to
  tcg. If the address is unaligned, a signal number (i.e., SIGBUS)
  should be raised.

  Regards
  Muhui

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