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  1. 09 May, 2024 17 commits
  3. 08 May, 2024 5 commits
    • Jose E. Marchesi's avatar
      bpf: Avoid uninitialized value in BPF_CORE_READ_BITFIELD · 00936709
      Jose E. Marchesi authored 
      [Changes from V1:
 - Use a default branch in the switch statement to initialize `val'.]

GCC warns that `val' may be used uninitialized in the
BPF_CRE_READ_BITFIELD macro, defined in bpf_core_read.h as:

	[...]
	unsigned long long val;						      \
	[...]								      \
	switch (__CORE_RELO(s, field, BYTE_SIZE)) {			      \
	case 1: val = *(const unsigned char *)p; break;			      \
	case 2: val = *(const unsigned short *)p; break;		      \
	case 4: val = *(const unsigned int *)p; break;			      \
	case 8: val = *(const unsigned long long *)p; break;		      \
        }       							      \
	[...]
	val;								      \
	}								      \

This patch adds a default entry in the switch statement that sets
`val' to zero in order to avoid the warning, and random values to be
used in case __builtin_preserve_field_info returns unexpected values
for BPF_FIELD_BYTE_SIZE.

Tested in bpf-next master.
No regressions.
Signed-off-by: default avatarJose E. Marchesi <jose.marchesi@oracle.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240508101313.16662-1-jose.marchesi@oracle.com
      00936709
    • Jose E. Marchesi's avatar
      bpf: guard BPF_NO_PRESERVE_ACCESS_INDEX in skb_pkt_end.c · 911edc69
      Jose E. Marchesi authored 
      This little patch is a follow-up to:
https://lore.kernel.org/bpf/20240507095011.15867-1-jose.marchesi@oracle.com/T/#u

The temporary workaround of passing -DBPF_NO_PRESERVE_ACCESS_INDEX
when building with GCC triggers a redefinition preprocessor error when
building progs/skb_pkt_end.c.  This patch adds a guard to avoid
redefinition.
Signed-off-by: default avatarJose E. Marchesi <jose.marchesi@oracle.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Acked-by: default avatarYonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240508110332.17332-1-jose.marchesi@oracle.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      911edc69
    • Jose E. Marchesi's avatar
      bpf: avoid UB in usages of the __imm_insn macro · 1209a523
      Jose E. Marchesi authored 
      [Changes from V2:
 - no-strict-aliasing is only applied when building with GCC.
 - cpumask_failure.c is excluded, as it doesn't use __imm_insn.]

The __imm_insn macro is defined in bpf_misc.h as:

  #define __imm_insn(name, expr) [name]"i"(*(long *)&(expr))

This may lead to type-punning and strict aliasing rules violations in
it's typical usage where the address of a struct bpf_insn is passed as
expr, like in:

  __imm_insn(st_mem,
             BPF_ST_MEM(BPF_W, BPF_REG_1, offsetof(struct __sk_buff, mark), 42))

Where:

  #define BPF_ST_MEM(SIZE, DST, OFF, IMM)				\
	((struct bpf_insn) {					\
		.code  = BPF_ST | BPF_SIZE(SIZE) | BPF_MEM,	\
		.dst_reg = DST,					\
		.src_reg = 0,					\
		.off   = OFF,					\
		.imm   = IMM })

In all the actual instances of this in the BPF selftests the value is
fed to a volatile asm statement as soon as it gets read from memory,
and thus it is unlikely anti-aliasing rules breakage may lead to
misguided optimizations.

However, GCC detects the potential problem (indirectly) by issuing a
warning stating that a temporary <Uxxxxxx> is used uninitialized,
where the temporary corresponds to the memory read by *(long *).

This patch adds -fno-strict-aliasing to the compilation flags of the
particular selftests that do type punning via __imm_insn, only for
GCC.

Tested in master bpf-next.
No regressions.
Signed-off-by: default avatarJose E. Marchesi <jose.marchesi@oracle.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: default avatarYonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240508103551.14955-1-jose.marchesi@oracle.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      1209a523
    • Jose E. Marchesi's avatar
      bpf: avoid uninitialized warnings in verifier_global_subprogs.c · cd3fc3b9
      Jose E. Marchesi authored 
      [Changes from V1:
- The warning to disable is -Wmaybe-uninitialized, not -Wuninitialized.
- This warning is only supported in GCC.]

The BPF selftest verifier_global_subprogs.c contains code that
purposedly performs out of bounds access to memory, to check whether
the kernel verifier is able to catch them.  For example:

  __noinline int global_unsupp(const int *mem)
  {
	if (!mem)
		return 0;
	return mem[100]; /* BOOM */
  }

With -O1 and higher and no inlining, GCC notices this fact and emits a
"maybe uninitialized" warning.  This is by design.  Note that the
emission of these warnings is highly dependent on the precise
optimizations that are performed.

This patch adds a compiler pragma to verifier_global_subprogs.c to
ignore these warnings.

Tested in bpf-next master.
No regressions.
Signed-off-by: default avatarJose E. Marchesi <jose.marchesi@oracle.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: default avatarYonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240507184756.1772-1-jose.marchesi@oracle.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      cd3fc3b9
    • Puranjay Mohan's avatar
      bpf, arm64: Add support for lse atomics in bpf_arena · e612b5c1
      Puranjay Mohan authored 
      When LSE atomics are available, BPF atomic instructions are implemented
as single ARM64 atomic instructions, therefore it is easy to enable
these in bpf_arena using the currently available exception handling
setup.

LL_SC atomics use loops and therefore would need more work to enable in
bpf_arena.

Enable LSE atomics based instructions in bpf_arena and use the
bpf_jit_supports_insn() callback to reject atomics in bpf_arena if LSE
atomics are not available.

All atomics and arena_atomics selftests are passing:

  [root@ip-172-31-2-216 bpf]# ./test_progs -a atomics,arena_atomics
  #3/1     arena_atomics/add:OK
  #3/2     arena_atomics/sub:OK
  #3/3     arena_atomics/and:OK
  #3/4     arena_atomics/or:OK
  #3/5     arena_atomics/xor:OK
  #3/6     arena_atomics/cmpxchg:OK
  #3/7     arena_atomics/xchg:OK
  #3       arena_atomics:OK
  #10/1    atomics/add:OK
  #10/2    atomics/sub:OK
  #10/3    atomics/and:OK
  #10/4    atomics/or:OK
  #10/5    atomics/xor:OK
  #10/6    atomics/cmpxchg:OK
  #10/7    atomics/xchg:OK
  #10      atomics:OK
  Summary: 2/14 PASSED, 0 SKIPPED, 0 FAILED
Signed-off-by: default avatarPuranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20240426161116.441-1-puranjay@kernel.orgSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      e612b5c1
  5. 07 May, 2024 18 commits
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