re: port-sparc/57594: openssl speed crashes on sparcv8

[matthew green <mrg%eterna.com.au@localhost>]

The following reply was made to PR port-sparc/57594; it has been noted by GNATS.

From: matthew green <mrg%eterna.com.au@localhost>
To: Martin Husemann <martin%duskware.de@localhost>
Cc: gnats-bugs%netbsd.org@localhost
Subject: re: port-sparc/57594: openssl speed crashes on sparcv8
Date: Thu, 31 Aug 2023 08:12:16 +1000

 Martin Husemann writes:
 > On Thu, Aug 31, 2023 at 05:47:13AM +1000, matthew green wrote:
 > > must be something in newer openssl that ends up leaving %y with
 > > 0x99 and wasn't hit before, as this bug is old.
 >
 > It is mostly random - and may only hit on some CPU implementations.
 > I have a patch (and an upstream bug report/pull request) that I will
 > commit soonish. With that I have been unable to reproduce the crash
 > in several runs.
 
 i wrote a simple program that reproduces it immediately:
 
 #include <stdio.h>
 #include <openssl/crypto.h>
 
 int
 main(void)
 {
         char largeish[32];
 
         printf("testing with 0 in %y\n");
         __asm __volatile("wr 0, %y");
         OPENSSL_cleanse(largeish, sizeof largeish);
 
         printf("testing with 0x99 in %y\n");
         __asm __volatile("wr 0x99, %y");
         OPENSSL_cleanse(largeish, sizeof largeish);
 }
 
 this patch fixes it:
 
 
 fix v8/v9 detection code for openssl.
 
 this code uses a trick where the encoding on both v8 and v9 are
 the same, and are not illegal instructions, but that the v9 one
 has a detectable difference than v8.
 
 the idea is that we perform a "subcc" (set condition codes) which
 sets "%ccr" on v9, which is an unimplemented "%asr2" on v8, then
 we read %ccr (v9) or %asr2 (v8), which will always be 0x99 on v9,
 and .. is non-trapping but impleentation defined on v8.
 
 for most implementations this returns the value of the %y reg.
 
 as nothing actually sets %y in this path, it remains the value it
 was most recently set to by something (anything), and if it just
 happens to be 0x99 then the v9 paths will be taken on v8.
 
 fix this by clearing the %y register before the potential read.
 
 fixes PR#57594.
 
 
 Index: crypto/external/bsd/openssl/dist/crypto/sparccpuid.S
 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
 RCS file: /cvsroot/src/crypto/external/bsd/openssl/dist/crypto/sparccpuid.=
 S,v
 retrieving revision 1.10
 diff -p -u -r1.10 sparccpuid.S
 --- crypto/external/bsd/openssl/dist/crypto/sparccpuid.S	7 May 2023 18:40:=
 16 -0000	1.10
 +++ crypto/external/bsd/openssl/dist/crypto/sparccpuid.S	30 Aug 2023 21:04=
 :12 -0000
 @@ -51,6 +51,10 @@ OPENSSL_wipe_cpu:
  	! to determine if the CPU the code is executing on is V8- or
  	! V9-compliant, as V9 returns a distinct value of 0x99,
  	! "negative" and "borrow" bits set in both %icc and %xcc.
 +	! XXXNETBSD PR#57594
 +	! we clear %y here in case it just happens to have 0x99 in it
 +	! and the v8 host takes the v9 path and faults.
 +	wr	0, %y
  	.word	0x91408000	!rd	%ccr,%o0
  	cmp	%o0,0x99
  	bne	.v8
 @@ -178,6 +182,10 @@ walk_reg_wins:
  OPENSSL_atomic_add:
  #ifndef ABI64
  	subcc	%g0,1,%o2
 +	! XXXNETBSD PR#57594
 +	! we clear %y here in case it just happens to have 0x99 in it
 +	! and the v8 host takes the v9 path and faults.
 +	wr	0, %y
  	.word	0x95408000	!rd	%ccr,%o2, see comment above
  	cmp	%o2,0x99
  	be	.v9
 @@ -226,6 +234,10 @@ OPENSSL_atomic_add:
  .align	32
  _sparcv9_rdtick:
  	subcc	%g0,1,%o0
 +	! XXXNETBSD PR#57594
 +	! we clear %y here in case it just happens to have 0x99 in it
 +	! and the v8 host takes the v9 path and faults.
 +	wr	0, %y
  	.word	0x91408000	!rd	%ccr,%o0
  	cmp	%o0,0x99
  	bne	.notick
 @@ -387,6 +399,10 @@ OPENSSL_cleanse:
  .Lot:
  #ifndef ABI64
  	subcc	%g0,1,%g1
 +	! XXXNETBSD PR#57594
 +	! we clear %y here in case it just happens to have 0x99 in it
 +	! and the v8 host takes the v9 path and faults.
 +	wr	0, %y
  	! see above for explanation
  	.word	0x83408000	!rd	%ccr,%g1
  	cmp	%g1,0x99