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  1. 12 Jul, 2024 3 commits
    • Shung-Hsi Yu's avatar
      bpf: use check_add_overflow() to check for addition overflows · 28a44110
      Shung-Hsi Yu authored 
      signed_add*_overflows() was added back when there was no overflow-check
helper. With the introduction of such helpers in commit f0907827
("compiler.h: enable builtin overflow checkers and add fallback code"), we
can drop signed_add*_overflows() in kernel/bpf/verifier.c and use the
generic check_add_overflow() instead.

This will make future refactoring easier, and takes advantage of
compiler-emitted hardware instructions that efficiently implement these
checks.

After the change GCC 13.3.0 generates cleaner assembly on x86_64:

	err = adjust_scalar_min_max_vals(env, insn, dst_reg, *src_reg);
   13625:	mov    0x28(%rbx),%r9  /*  r9 = src_reg->smin_value */
   13629:	mov    0x30(%rbx),%rcx /* rcx = src_reg->smax_value */
   ...
	if (check_add_overflow(*dst_smin, src_reg->smin_value, dst_smin) ||
   141c1:	mov    %r9,%rax
   141c4:	add    0x28(%r12),%rax
   141c9:	mov    %rax,0x28(%r12)
   141ce:	jo     146e4 <adjust_reg_min_max_vals+0x1294>
	    check_add_overflow(*dst_smax, src_reg->smax_value, dst_smax)) {
   141d4:	add    0x30(%r12),%rcx
   141d9:	mov    %rcx,0x30(%r12)
	if (check_add_overflow(*dst_smin, src_reg->smin_value, dst_smin) ||
   141de:	jo     146e4 <adjust_reg_min_max_vals+0x1294>
   ...
		*dst_smin = S64_MIN;
   146e4:	movabs $0x8000000000000000,%rax
   146ee:	mov    %rax,0x28(%r12)
		*dst_smax = S64_MAX;
   146f3:	sub    $0x1,%rax
   146f7:	mov    %rax,0x30(%r12)

Before the change it gives:

	s64 smin_val = src_reg->smin_value;
     675:	mov    0x28(%rsi),%r8
	s64 smax_val = src_reg->smax_value;
	u64 umin_val = src_reg->umin_value;
	u64 umax_val = src_reg->umax_value;
     679:	mov    %rdi,%rax /* rax = dst_reg */
	if (signed_add_overflows(dst_reg->smin_value, smin_val) ||
     67c:	mov    0x28(%rdi),%rdi /* rdi = dst_reg->smin_value */
	u64 umin_val = src_reg->umin_value;
     680:	mov    0x38(%rsi),%rdx
	u64 umax_val = src_reg->umax_value;
     684:	mov    0x40(%rsi),%rcx
	s64 res = (s64)((u64)a + (u64)b);
     688:	lea    (%r8,%rdi,1),%r9 /* r9 = dst_reg->smin_value + src_reg->smin_value */
	return res < a;
     68c:	cmp    %r9,%rdi
     68f:	setg   %r10b /* r10b = (dst_reg->smin_value + src_reg->smin_value) > dst_reg->smin_value */
	if (b < 0)
     693:	test   %r8,%r8
     696:	js     72b <scalar_min_max_add+0xbb>
	    signed_add_overflows(dst_reg->smax_value, smax_val)) {
		dst_reg->smin_value = S64_MIN;
		dst_reg->smax_value = S64_MAX;
     69c:	movabs $0x7fffffffffffffff,%rdi
	s64 smax_val = src_reg->smax_value;
     6a6:	mov    0x30(%rsi),%r8
		dst_reg->smin_value = S64_MIN;
     6aa:	00 00 00 	movabs $0x8000000000000000,%rsi
	if (signed_add_overflows(dst_reg->smin_value, smin_val) ||
     6b4:	test   %r10b,%r10b /* (dst_reg->smin_value + src_reg->smin_value) > dst_reg->smin_value ? goto 6cb */
     6b7:	jne    6cb <scalar_min_max_add+0x5b>
	    signed_add_overflows(dst_reg->smax_value, smax_val)) {
     6b9:	mov    0x30(%rax),%r10   /* r10 = dst_reg->smax_value */
	s64 res = (s64)((u64)a + (u64)b);
     6bd:	lea    (%r10,%r8,1),%r11 /* r11 = dst_reg->smax_value + src_reg->smax_value */
	if (b < 0)
     6c1:	test   %r8,%r8
     6c4:	js     71e <scalar_min_max_add+0xae>
	if (signed_add_overflows(dst_reg->smin_value, smin_val) ||
     6c6:	cmp    %r11,%r10 /* (dst_reg->smax_value + src_reg->smax_value) <= dst_reg->smax_value ? goto 723 */
     6c9:	jle    723 <scalar_min_max_add+0xb3>
	} else {
		dst_reg->smin_value += smin_val;
		dst_reg->smax_value += smax_val;
	}
     6cb:	mov    %rsi,0x28(%rax)
     ...
     6d5:	mov    %rdi,0x30(%rax)
     ...
	if (signed_add_overflows(dst_reg->smin_value, smin_val) ||
     71e:	cmp    %r11,%r10
     721:	jl     6cb <scalar_min_max_add+0x5b>
		dst_reg->smin_value += smin_val;
     723:	mov    %r9,%rsi
		dst_reg->smax_value += smax_val;
     726:	mov    %r11,%rdi
     729:	jmp    6cb <scalar_min_max_add+0x5b>
		return res > a;
     72b:	cmp    %r9,%rdi
     72e:	setl   %r10b
     732:	jmp    69c <scalar_min_max_add+0x2c>
     737:	nopw   0x0(%rax,%rax,1)

Note: unlike adjust_ptr_min_max_vals() and scalar*_min_max_add(), it is
necessary to introduce intermediate variable in adjust_jmp_off() to keep
the functional behavior unchanged. Without an intermediate variable
imm/off will be altered even on overflow.
Suggested-by: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarShung-Hsi Yu <shung-hsi.yu@suse.com>
Link: https://lore.kernel.org/r/20240712080127.136608-3-shung-hsi.yu@suse.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      28a44110
    • Shung-Hsi Yu's avatar
      bpf: fix overflow check in adjust_jmp_off() · 4a04b4f0
      Shung-Hsi Yu authored 
      adjust_jmp_off() incorrectly used the insn->imm field for all overflow check,
which is incorrect as that should only be done or the BPF_JMP32 | BPF_JA case,
not the general jump instruction case. Fix it by using insn->off for overflow
check in the general case.

Fixes: 5337ac4c ("bpf: Fix the corner case with may_goto and jump to the 1st insn.")
Signed-off-by: default avatarShung-Hsi Yu <shung-hsi.yu@suse.com>
Link: https://lore.kernel.org/r/20240712080127.136608-2-shung-hsi.yu@suse.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      4a04b4f0
    • Alan Maguire's avatar
      bpf: Eliminate remaining "make W=1" warnings in kernel/bpf/btf.o · 2454075f
      Alan Maguire authored 
      As reported by Mirsad [1] we still see format warnings in kernel/bpf/btf.o
at W=1 warning level:

  CC      kernel/bpf/btf.o
./kernel/bpf/btf.c: In function ‘btf_type_seq_show_flags’:
./kernel/bpf/btf.c:7553:21: warning: assignment left-hand side might be a candidate for a format attribute [-Wsuggest-attribute=format]
 7553 |         sseq.showfn = btf_seq_show;
      |                     ^
./kernel/bpf/btf.c: In function ‘btf_type_snprintf_show’:
./kernel/bpf/btf.c:7604:31: warning: assignment left-hand side might be a candidate for a format attribute [-Wsuggest-attribute=format]
 7604 |         ssnprintf.show.showfn = btf_snprintf_show;
      |                               ^

Combined with CONFIG_WERROR=y these can halt the build.

The fix (annotating the structure field with __printf())
suggested by Mirsad resolves these. Apologies I missed this last time.
No other W=1 warnings were observed in kernel/bpf after this fix.

[1] https://lore.kernel.org/bpf/92c9d047-f058-400c-9c7d-81d4dc1ef71b@gmail.com/

Fixes: b3470da3 ("bpf: annotate BTF show functions with __printf")
Reported-by: default avatarMirsad Todorovac <mtodorovac69@gmail.com>
Suggested-by: default avatarMirsad Todorovac <mtodorovac69@gmail.com>
Signed-off-by: default avatarAlan Maguire <alan.maguire@oracle.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240712092859.1390960-1-alan.maguire@oracle.com
      2454075f
  3. 11 Jul, 2024 2 commits
  5. 10 Jul, 2024 17 commits
  7. 09 Jul, 2024 18 commits
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