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[Bug 1859713] Re: ARM v8.3a pauth not working

From: Vincent Dehors
Subject: [Bug 1859713] Re: ARM v8.3a pauth not working
Date: Thu, 16 Jan 2020 20:47:05 -0000


Here is a patch for this bug. The sbox function was using "b+=16"
instead of "b+=4".

Also, you check test vector using :

    uint64_t P = 0xfb623599da6e8127ull;
    uint64_t T = 0x477d469dec0b8762ull;
    uint64_t w0 = 0x84be85ce9804e94bull;
    uint64_t k0 = 0xec2802d4e0a488e9ull;
    ARMPACKey key = { .hi = w0, .lo = k0 };
    uint64_t C5 = pauth_computepac(P, T, key);
    /* C5 should be 0xc003b93999b33765 */

** Patch added: "0001-target-arm-Fix-PAuth-sbox-functions.patch"

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  ARM v8.3a pauth not working

Status in QEMU:

Bug description:
  Host: Ubuntu 19.10 - x86_64 machine
  QEMU version: 3a63b24a1bbf166e6f455fe43a6bbd8dea413d92 (master)

  ARMV8.3 pauth is not working well.

  With a test code containing two pauth instructions:
      - paciasp that sign LR with A key and sp as context;
      - autiasp that verify the signature.

      - Run the program and corrupt LR just before autiasp (ex 0x3e00000400660 
instead of 0x3e000000400664)

      - autiasp places an invalid pointer in LR

      - autiasp successfully auth the pointer and places 0x0400660 in LR.

  Further explanations:
      Adding traces in qemu code shows that "pauth_computepac" is not robust 
enough against truncating.
      With 0x31000000400664 as input of pauth_auth, we obtain 
"0x55b1d65b2c138e14" for PAC, "0x30" for bot_bit and "0x38" for top_bit.
      With 0x310040008743ec as input of pauth (with same key), we obtain 
"0x55b1d65b2c138ef4" for PAC, "0x30" for bot_bit and "0x38" for top_bit.
      Values of top_bit and bottom_bit are strictly the same and it should not.

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