ubsan: Move INT_MIN / -1 instrumentation from -fsanitize=integer-divide-by-zero to -fsanitize=signed-integer-overflow [PR102515]

  Hi!

As noted by Richi, in clang INT_MIN / -1 is instrumented under
-fsanitize=signed-integer-overflow rather than
-fsanitize=integer-divide-by-zero as we did and doing it in the former
makes more sense, as it is overflow during division rather than division
by zero.
I've verified on godbolt that clang behaved that way since 3.2-ish times or
so when sanitizers were added.
Furthermore, we've been using
-f{,no-}sanitize-recover=integer-divide-by-zero to decide on the float
-fsanitize=float-divide-by-zero instrumentation _abort suffix.
The case where INT_MIN / -1 is instrumented by one sanitizer and
x / 0 by another one when both are enabled is slightly harder if
the -f{,no-}sanitize-recover={integer-divide-by-zero,signed-integer-overflow}
flags differ, then we need to emit both __ubsan_handle_divrem_overflow
and __ubsan_handle_divrem_overflow_abort calls guarded by their respective
checks rather than one guarded by check1 || check2.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2021-10-01  Jakub Jelinek  <jakub@redhat.com>
	    Richard Biener  <rguenther@suse.de>

	PR sanitizer/102515
gcc/
	* doc/invoke.texi (-fsanitize=integer-divide-by-zero): Remove
	INT_MIN / -1 division detection from here ...
	(-fsanitize=signed-integer-overflow): ... and add it here.
gcc/c-family/
	* c-ubsan.c (ubsan_instrument_division): Check the right
	flag_sanitize_recover bit, depending on which sanitization
	is done.  Sanitize INT_MIN / -1 under SANITIZE_SI_OVERFLOW
	rather than SANITIZE_DIVIDE.  If both SANITIZE_SI_OVERFLOW
	and SANITIZE_DIVIDE is enabled, neither check is known
	to be false and flag_sanitize_recover bits for those two
	aren't the same, emit both __ubsan_handle_divrem_overflow
	and __ubsan_handle_divrem_overflow_abort calls.
gcc/c/
	* c-typeck.c (build_binary_op): Call ubsan_instrument_division
	for division even for SANITIZE_SI_OVERFLOW.
gcc/cp/
	* typeck.c (cp_build_binary_op): Call ubsan_instrument_division
	for division even for SANITIZE_SI_OVERFLOW.
gcc/testsuite/
	* c-c++-common/ubsan/div-by-zero-3.c: Use
	-fsanitize=signed-integer-overflow instead of
	-fsanitize=integer-divide-by-zero.
	* c-c++-common/ubsan/div-by-zero-5.c: Likewise.
	* c-c++-common/ubsan/div-by-zero-4.c: Likewise.  Add
	-fsanitize-undefined-trap-on-error.
	* c-c++-common/ubsan/float-div-by-zero-2.c: New test.
	* c-c++-common/ubsan/overflow-div-1.c: New test.
	* c-c++-common/ubsan/overflow-div-2.c: New test.
	* c-c++-common/ubsan/overflow-div-3.c: New test.


	Jakub
  

On Fri, 1 Oct 2021, Jakub Jelinek wrote:

> Hi!
> 
> As noted by Richi, in clang INT_MIN / -1 is instrumented under
> -fsanitize=signed-integer-overflow rather than
> -fsanitize=integer-divide-by-zero as we did and doing it in the former
> makes more sense, as it is overflow during division rather than division
> by zero.
> I've verified on godbolt that clang behaved that way since 3.2-ish times or
> so when sanitizers were added.
> Furthermore, we've been using
> -f{,no-}sanitize-recover=integer-divide-by-zero to decide on the float
> -fsanitize=float-divide-by-zero instrumentation _abort suffix.
> The case where INT_MIN / -1 is instrumented by one sanitizer and
> x / 0 by another one when both are enabled is slightly harder if
> the -f{,no-}sanitize-recover={integer-divide-by-zero,signed-integer-overflow}
> flags differ, then we need to emit both __ubsan_handle_divrem_overflow
> and __ubsan_handle_divrem_overflow_abort calls guarded by their respective
> checks rather than one guarded by check1 || check2.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.  Maybe the change is worth mentioning in changes.html or maybe it's
just a bugfix...

Thanks,
Richard.

> 2021-10-01  Jakub Jelinek  <jakub@redhat.com>
> 	    Richard Biener  <rguenther@suse.de>
> 
> 	PR sanitizer/102515
> gcc/
> 	* doc/invoke.texi (-fsanitize=integer-divide-by-zero): Remove
> 	INT_MIN / -1 division detection from here ...
> 	(-fsanitize=signed-integer-overflow): ... and add it here.
> gcc/c-family/
> 	* c-ubsan.c (ubsan_instrument_division): Check the right
> 	flag_sanitize_recover bit, depending on which sanitization
> 	is done.  Sanitize INT_MIN / -1 under SANITIZE_SI_OVERFLOW
> 	rather than SANITIZE_DIVIDE.  If both SANITIZE_SI_OVERFLOW
> 	and SANITIZE_DIVIDE is enabled, neither check is known
> 	to be false and flag_sanitize_recover bits for those two
> 	aren't the same, emit both __ubsan_handle_divrem_overflow
> 	and __ubsan_handle_divrem_overflow_abort calls.
> gcc/c/
> 	* c-typeck.c (build_binary_op): Call ubsan_instrument_division
> 	for division even for SANITIZE_SI_OVERFLOW.
> gcc/cp/
> 	* typeck.c (cp_build_binary_op): Call ubsan_instrument_division
> 	for division even for SANITIZE_SI_OVERFLOW.
> gcc/testsuite/
> 	* c-c++-common/ubsan/div-by-zero-3.c: Use
> 	-fsanitize=signed-integer-overflow instead of
> 	-fsanitize=integer-divide-by-zero.
> 	* c-c++-common/ubsan/div-by-zero-5.c: Likewise.
> 	* c-c++-common/ubsan/div-by-zero-4.c: Likewise.  Add
> 	-fsanitize-undefined-trap-on-error.
> 	* c-c++-common/ubsan/float-div-by-zero-2.c: New test.
> 	* c-c++-common/ubsan/overflow-div-1.c: New test.
> 	* c-c++-common/ubsan/overflow-div-2.c: New test.
> 	* c-c++-common/ubsan/overflow-div-3.c: New test.
> 
> --- gcc/doc/invoke.texi.jj	2021-09-29 10:07:41.841880681 +0200
> +++ gcc/doc/invoke.texi	2021-09-30 20:21:37.736147295 +0200
> @@ -15229,7 +15229,7 @@ ISO C90 and C99, etc.
>  
>  @item -fsanitize=integer-divide-by-zero
>  @opindex fsanitize=integer-divide-by-zero
> -Detect integer division by zero as well as @code{INT_MIN / -1} division.
> +Detect integer division by zero.
>  
>  @item -fsanitize=unreachable
>  @opindex fsanitize=unreachable
> @@ -15261,7 +15261,8 @@ returning a value.  This option works in
>  @opindex fsanitize=signed-integer-overflow
>  This option enables signed integer overflow checking.  We check that
>  the result of @code{+}, @code{*}, and both unary and binary @code{-}
> -does not overflow in the signed arithmetics.  Note, integer promotion
> +does not overflow in the signed arithmetics.  This also detects
> +@code{INT_MIN / -1} signed division.  Note, integer promotion
>  rules must be taken into account.  That is, the following is not an
>  overflow:
>  @smallexample
> --- gcc/c-family/c-ubsan.c.jj	2021-01-04 10:25:50.355103357 +0100
> +++ gcc/c-family/c-ubsan.c	2021-09-30 20:18:53.273433013 +0200
> @@ -39,8 +39,9 @@ along with GCC; see the file COPYING3.
>  tree
>  ubsan_instrument_division (location_t loc, tree op0, tree op1)
>  {
> -  tree t, tt;
> +  tree t, tt, x = NULL_TREE;
>    tree type = TREE_TYPE (op0);
> +  enum sanitize_code flag = SANITIZE_DIVIDE;
>  
>    /* At this point both operands should have the same type,
>       because they are already converted to RESULT_TYPE.
> @@ -58,24 +59,42 @@ ubsan_instrument_division (location_t lo
>  		     op1, build_int_cst (type, 0));
>    else if (TREE_CODE (type) == REAL_TYPE
>  	   && sanitize_flags_p (SANITIZE_FLOAT_DIVIDE))
> -    t = fold_build2 (EQ_EXPR, boolean_type_node,
> -		     op1, build_real (type, dconst0));
> +    {
> +      t = fold_build2 (EQ_EXPR, boolean_type_node,
> +		       op1, build_real (type, dconst0));
> +      flag = SANITIZE_FLOAT_DIVIDE;
> +    }
>    else
> -    return NULL_TREE;
> +    t = NULL_TREE;
>  
>    /* We check INT_MIN / -1 only for signed types.  */
>    if (TREE_CODE (type) == INTEGER_TYPE
> -      && sanitize_flags_p (SANITIZE_DIVIDE)
> +      && sanitize_flags_p (SANITIZE_SI_OVERFLOW)
>        && !TYPE_UNSIGNED (type))
>      {
> -      tree x;
>        tt = fold_build2 (EQ_EXPR, boolean_type_node, unshare_expr (op1),
>  			build_int_cst (type, -1));
>        x = fold_build2 (EQ_EXPR, boolean_type_node, op0,
>  		       TYPE_MIN_VALUE (type));
>        x = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, x, tt);
> -      t = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, t, x);
> +      if (t == NULL_TREE || integer_zerop (t))
> +	{
> +	  t = x;
> +	  x = NULL_TREE;
> +	  flag = SANITIZE_SI_OVERFLOW;
> +	}
> +      else if (flag_sanitize_undefined_trap_on_error
> +	       || (((flag_sanitize_recover & SANITIZE_DIVIDE) == 0)
> +		   == ((flag_sanitize_recover & SANITIZE_SI_OVERFLOW) == 0)))
> +	{
> +	  t = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, t, x);
> +	  x = NULL_TREE;
> +	}
> +      else if (integer_zerop (x))
> +	x = NULL_TREE;
>      }
> +  else if (t == NULL_TREE)
> +    return NULL_TREE;
>  
>    /* If the condition was folded to 0, no need to instrument
>       this expression.  */
> @@ -95,7 +114,7 @@ ubsan_instrument_division (location_t lo
>  				     NULL_TREE);
>        data = build_fold_addr_expr_loc (loc, data);
>        enum built_in_function bcode
> -	= (flag_sanitize_recover & SANITIZE_DIVIDE)
> +	= (flag_sanitize_recover & flag)
>  	  ? BUILT_IN_UBSAN_HANDLE_DIVREM_OVERFLOW
>  	  : BUILT_IN_UBSAN_HANDLE_DIVREM_OVERFLOW_ABORT;
>        tt = builtin_decl_explicit (bcode);
> @@ -103,8 +122,20 @@ ubsan_instrument_division (location_t lo
>        op1 = unshare_expr (op1);
>        tt = build_call_expr_loc (loc, tt, 3, data, ubsan_encode_value (op0),
>  				ubsan_encode_value (op1));
> +      if (x)
> +	{
> +	  bcode = (flag_sanitize_recover & SANITIZE_SI_OVERFLOW)
> +		  ? BUILT_IN_UBSAN_HANDLE_DIVREM_OVERFLOW
> +		  : BUILT_IN_UBSAN_HANDLE_DIVREM_OVERFLOW_ABORT;
> +	  tree xt = builtin_decl_explicit (bcode);
> +	  op0 = unshare_expr (op0);
> +	  op1 = unshare_expr (op1);
> +	  xt = build_call_expr_loc (loc, xt, 3, data, ubsan_encode_value (op0),
> +				    ubsan_encode_value (op1));
> +	  x = fold_build3 (COND_EXPR, void_type_node, x, xt, void_node);
> +	}
>      }
> -  t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_node);
> +  t = fold_build3 (COND_EXPR, void_type_node, t, tt, x ? x : void_node);
>  
>    return t;
>  }
> --- gcc/c/c-typeck.c.jj	2021-09-29 10:07:41.789881404 +0200
> +++ gcc/c/c-typeck.c	2021-09-30 20:50:00.990465683 +0200
> @@ -12733,7 +12733,9 @@ build_binary_op (location_t location, en
>      }
>  
>    if (sanitize_flags_p ((SANITIZE_SHIFT
> -			 | SANITIZE_DIVIDE | SANITIZE_FLOAT_DIVIDE))
> +			 | SANITIZE_DIVIDE
> +			 | SANITIZE_FLOAT_DIVIDE
> +			 | SANITIZE_SI_OVERFLOW))
>        && current_function_decl != NULL_TREE
>        && (doing_div_or_mod || doing_shift)
>        && !require_constant_value)
> @@ -12744,7 +12746,8 @@ build_binary_op (location_t location, en
>        op0 = c_fully_fold (op0, false, NULL);
>        op1 = c_fully_fold (op1, false, NULL);
>        if (doing_div_or_mod && (sanitize_flags_p ((SANITIZE_DIVIDE
> -						  | SANITIZE_FLOAT_DIVIDE))))
> +						  | SANITIZE_FLOAT_DIVIDE
> +						  | SANITIZE_SI_OVERFLOW))))
>  	instrument_expr = ubsan_instrument_division (location, op0, op1);
>        else if (doing_shift && sanitize_flags_p (SANITIZE_SHIFT))
>  	instrument_expr = ubsan_instrument_shift (location, code, op0, op1);
> --- gcc/cp/typeck.c.jj	2021-09-09 10:40:26.096175666 +0200
> +++ gcc/cp/typeck.c	2021-09-30 20:50:23.806147945 +0200
> @@ -6038,7 +6038,9 @@ cp_build_binary_op (const op_location_t
>      }
>  
>    if (sanitize_flags_p ((SANITIZE_SHIFT
> -			 | SANITIZE_DIVIDE | SANITIZE_FLOAT_DIVIDE))
> +			 | SANITIZE_DIVIDE
> +			 | SANITIZE_FLOAT_DIVIDE
> +			 | SANITIZE_SI_OVERFLOW))
>        && current_function_decl != NULL_TREE
>        && !processing_template_decl
>        && (doing_div_or_mod || doing_shift))
> @@ -6050,7 +6052,9 @@ cp_build_binary_op (const op_location_t
>        op1 = fold_non_dependent_expr (op1, complain);
>        tree instrument_expr1 = NULL_TREE;
>        if (doing_div_or_mod
> -	  && sanitize_flags_p (SANITIZE_DIVIDE | SANITIZE_FLOAT_DIVIDE))
> +	  && sanitize_flags_p (SANITIZE_DIVIDE
> +			       | SANITIZE_FLOAT_DIVIDE
> +			       | SANITIZE_SI_OVERFLOW))
>  	{
>  	  /* For diagnostics we want to use the promoted types without
>  	     shorten_binary_op.  So convert the arguments to the
> --- gcc/testsuite/c-c++-common/ubsan/div-by-zero-3.c.jj	2020-01-12 11:54:37.029404115 +0100
> +++ gcc/testsuite/c-c++-common/ubsan/div-by-zero-3.c	2021-09-30 20:51:00.522636616 +0200
> @@ -1,5 +1,5 @@
>  /* { dg-do run } */
> -/* { dg-options "-fsanitize=integer-divide-by-zero -Wno-overflow" } */
> +/* { dg-options "-fsanitize=signed-integer-overflow -Wno-overflow" } */
>  
>  #include <limits.h>
>  
> --- gcc/testsuite/c-c++-common/ubsan/div-by-zero-4.c.jj	2020-01-12 11:54:37.029404115 +0100
> +++ gcc/testsuite/c-c++-common/ubsan/div-by-zero-4.c	2021-09-30 20:24:17.051933114 +0200
> @@ -1,5 +1,5 @@
>  /* { dg-do run } */
> -/* { dg-options "-fsanitize=integer-divide-by-zero -Wno-overflow" } */
> +/* { dg-options "-fsanitize=signed-integer-overflow -fsanitize-undefined-trap-on-error -Wno-overflow" } */
>  
>  #define INT_MIN (-__INT_MAX__ - 1)
>  
> --- gcc/testsuite/c-c++-common/ubsan/div-by-zero-5.c.jj	2020-01-12 11:54:37.029404115 +0100
> +++ gcc/testsuite/c-c++-common/ubsan/div-by-zero-5.c	2021-09-30 20:24:55.559397933 +0200
> @@ -1,5 +1,5 @@
>  /* { dg-do compile } */
> -/* { dg-options "-fsanitize=integer-divide-by-zero" } */
> +/* { dg-options "-fsanitize=signed-integer-overflow" } */
>  
>  void
>  foo (void)
> --- gcc/testsuite/c-c++-common/ubsan/float-div-by-zero-2.c.jj	2021-10-01 12:28:23.485086791 +0200
> +++ gcc/testsuite/c-c++-common/ubsan/float-div-by-zero-2.c	2021-10-01 12:29:35.875062499 +0200
> @@ -0,0 +1,18 @@
> +/* { dg-do run } */
> +/* { dg-shouldfail "ubsan" } */
> +/* { dg-options "-fsanitize=float-divide-by-zero -fno-sanitize-recover=float-divide-by-zero -fsanitize-recover=integer-divide-by-zero" } */
> +
> +int
> +main (void)
> +{
> +  volatile float a = 1.3f;
> +  volatile double b = 0.0;
> +  volatile int c = 4;
> +  volatile float res;
> +
> +  res = a / b;
> +
> +  return 0;
> +}
> +
> +/* { dg-output "division by zero" } */
> --- gcc/testsuite/c-c++-common/ubsan/overflow-div-1.c.jj	2021-10-01 12:30:48.269038146 +0200
> +++ gcc/testsuite/c-c++-common/ubsan/overflow-div-1.c	2021-10-01 12:31:49.532171295 +0200
> @@ -0,0 +1,17 @@
> +/* { dg-do run } */
> +/* { dg-options "-fsanitize=integer-divide-by-zero -fno-sanitize-recover=undefined,float-divide-by-zero -Wno-overflow" } */
> +
> +#include <limits.h>
> +
> +int
> +main (void)
> +{
> +  volatile int min = INT_MIN;
> +  volatile int zero = 0;
> +
> +  INT_MIN / -1;
> +  min / -1;
> +  min / (10 * zero - (2 - 1));
> +
> +  return 0;
> +}
> --- gcc/testsuite/c-c++-common/ubsan/overflow-div-2.c.jj	2021-10-01 12:34:28.814917433 +0200
> +++ gcc/testsuite/c-c++-common/ubsan/overflow-div-2.c	2021-10-01 12:50:24.398395074 +0200
> @@ -0,0 +1,41 @@
> +/* { dg-do run { target *-*-linux* *-*-gnu* } } */
> +/* { dg-shouldfail "ubsan" } */
> +/* { dg-options "-fsanitize=undefined -fno-sanitize-recover=integer-divide-by-zero" } */
> +
> +#include <limits.h>
> +#include <signal.h>
> +#include <stdlib.h>
> +
> +int cnt;
> +
> +__attribute__((noipa)) int
> +foo (int x, int y)
> +{
> +  return x / y;
> +}
> +
> +void
> +handler (int i)
> +{
> +  if (cnt++ != 0)
> +    exit (0);
> +  volatile int b = foo (5, 0);
> +  exit (0);
> +}
> +
> +int
> +main (void)
> +{
> +  struct sigaction s;
> +  sigemptyset (&s.sa_mask);
> +  s.sa_handler = handler;
> +  s.sa_flags = 0;
> +  sigaction (SIGFPE, &s, NULL);
> +  volatile int a = foo (INT_MIN, -1);
> +  cnt++;
> +  volatile int b = foo (5, 0);
> +  return 0;
> +}
> +
> +/* { dg-output "division of -2147483648 by -1 cannot be represented in type 'int'\[^\n\r]*(\n|\r\n|\r)" } */
> +/* { dg-output "\[^\n\r]*division by zero\[^\n\r]*" } */
> --- gcc/testsuite/c-c++-common/ubsan/overflow-div-3.c.jj	2021-10-01 12:39:28.230680432 +0200
> +++ gcc/testsuite/c-c++-common/ubsan/overflow-div-3.c	2021-10-01 12:50:58.652910346 +0200
> @@ -0,0 +1,41 @@
> +/* { dg-do run { target *-*-linux* *-*-gnu* } } */
> +/* { dg-shouldfail "ubsan" } */
> +/* { dg-options "-fsanitize=undefined -fno-sanitize-recover=signed-integer-overflow" } */
> +
> +#include <limits.h>
> +#include <signal.h>
> +#include <stdlib.h>
> +
> +int cnt;
> +
> +__attribute__((noipa)) int
> +foo (int x, int y)
> +{
> +  return x / y;
> +}
> +
> +void
> +handler (int i)
> +{
> +  if (cnt++ != 0)
> +    exit (0);
> +  volatile int b = foo (INT_MIN, -1);
> +  exit (0);
> +}
> +
> +int
> +main (void)
> +{
> +  struct sigaction s;
> +  sigemptyset (&s.sa_mask);
> +  s.sa_handler = handler;
> +  s.sa_flags = 0;
> +  sigaction (SIGFPE, &s, NULL);
> +  volatile int a = foo (42, 0);
> +  cnt++;
> +  volatile int b = foo (INT_MIN, -1);
> +  return 0;
> +}
> +
> +/* { dg-output "division by zero\[^\n\r]*(\n|\r\n|\r)" } */
> +/* { dg-output "\[^\n\r]*division of -2147483648 by -1 cannot be represented in type 'int'" } */
> 
> 	Jakub
> 
>
  

On Fri, Oct 01, 2021 at 01:53:37PM +0200, Richard Biener wrote:
> OK.  Maybe the change is worth mentioning in changes.html or maybe it's
> just a bugfix...

I think it is worth mentioning it there.
And so I'd probably wouldn't try to backport it, except perhaps
the recover for float-divide-by-zero fix.

	Jakub