From: Andrii Nakryiko <andrii@kernel.org>
To: <bpf@vger.kernel.org>, <ast@kernel.org>, <daniel@iogearbox.net>,
<martin.lau@kernel.org>
Cc: <andrii@kernel.org>, <kernel-team@meta.com>,
Eduard Zingerman <eddyz87@gmail.com>
Subject: [PATCH v6 bpf-next 17/17] bpf: generalize reg_set_min_max() to handle two sets of two registers
Date: Wed, 1 Nov 2023 20:37:59 -0700 [thread overview]
Message-ID: <20231102033759.2541186-18-andrii@kernel.org> (raw)
In-Reply-To: <20231102033759.2541186-1-andrii@kernel.org>
Change reg_set_min_max() to take FALSE/TRUE sets of two registers each,
instead of assuming that we are always comparing to a constant. For now
we still assume that right-hand side registers are constants (and make
sure that's the case by swapping src/dst regs, if necessary), but
subsequent patches will remove this limitation.
reg_set_min_max() is now called unconditionally for any register
comparison, so that might include pointer vs pointer. This makes it
consistent with is_branch_taken() generality. But we currently only
support adjustments based on SCALAR vs SCALAR comparisons, so
reg_set_min_max() has to guard itself againts pointers.
Taking two by two registers allows to further unify and simplify
check_cond_jmp_op() logic. We utilize fake register for BPF_K
conditional jump case, just like with is_branch_taken() part.
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
kernel/bpf/verifier.c | 131 ++++++++++++++++++------------------------
1 file changed, 56 insertions(+), 75 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 438bf96b1c2d..2197385d91dc 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -14379,32 +14379,50 @@ static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg
return is_scalar_branch_taken(reg1, reg2, opcode, is_jmp32);
}
-/* Adjusts the register min/max values in the case that the dst_reg is the
- * variable register that we are working on, and src_reg is a constant or we're
- * simply doing a BPF_K check.
- * In JEQ/JNE cases we also adjust the var_off values.
+/* Adjusts the register min/max values in the case that the dst_reg and
+ * src_reg are both SCALAR_VALUE registers (or we are simply doing a BPF_K
+ * check, in which case we havea fake SCALAR_VALUE representing insn->imm).
+ * Technically we can do similar adjustments for pointers to the same object,
+ * but we don't support that right now.
*/
static void reg_set_min_max(struct bpf_reg_state *true_reg1,
+ struct bpf_reg_state *true_reg2,
struct bpf_reg_state *false_reg1,
- u64 uval, u32 uval32,
+ struct bpf_reg_state *false_reg2,
u8 opcode, bool is_jmp32)
{
- struct tnum false_32off = tnum_subreg(false_reg1->var_off);
- struct tnum false_64off = false_reg1->var_off;
- struct tnum true_32off = tnum_subreg(true_reg1->var_off);
- struct tnum true_64off = true_reg1->var_off;
- s64 sval = (s64)uval;
- s32 sval32 = (s32)uval32;
-
- /* If the dst_reg is a pointer, we can't learn anything about its
- * variable offset from the compare (unless src_reg were a pointer into
- * the same object, but we don't bother with that.
- * Since false_reg1 and true_reg1 have the same type by construction, we
- * only need to check one of them for pointerness.
+ struct tnum false_32off, false_64off;
+ struct tnum true_32off, true_64off;
+ u64 uval;
+ u32 uval32;
+ s64 sval;
+ s32 sval32;
+
+ /* If either register is a pointer, we can't learn anything about its
+ * variable offset from the compare (unless they were a pointer into
+ * the same object, but we don't bother with that).
*/
- if (__is_pointer_value(false, false_reg1))
+ if (false_reg1->type != SCALAR_VALUE || false_reg2->type != SCALAR_VALUE)
+ return;
+
+ /* we expect right-hand registers (src ones) to be constants, for now */
+ if (!is_reg_const(false_reg2, is_jmp32)) {
+ opcode = flip_opcode(opcode);
+ swap(true_reg1, true_reg2);
+ swap(false_reg1, false_reg2);
+ }
+ if (!is_reg_const(false_reg2, is_jmp32))
return;
+ false_32off = tnum_subreg(false_reg1->var_off);
+ false_64off = false_reg1->var_off;
+ true_32off = tnum_subreg(true_reg1->var_off);
+ true_64off = true_reg1->var_off;
+ uval = false_reg2->var_off.value;
+ uval32 = (u32)tnum_subreg(false_reg2->var_off).value;
+ sval = (s64)uval;
+ sval32 = (s32)uval32;
+
switch (opcode) {
/* JEQ/JNE comparison doesn't change the register equivalence.
*
@@ -14541,22 +14559,6 @@ static void reg_set_min_max(struct bpf_reg_state *true_reg1,
}
}
-/* Same as above, but for the case that dst_reg holds a constant and src_reg is
- * the variable reg.
- */
-static void reg_set_min_max_inv(struct bpf_reg_state *true_reg,
- struct bpf_reg_state *false_reg,
- u64 uval, u32 uval32,
- u8 opcode, bool is_jmp32)
-{
- opcode = flip_opcode(opcode);
- /* This uses zero as "not present in table"; luckily the zero opcode,
- * BPF_JA, can't get here.
- */
- if (opcode)
- reg_set_min_max(true_reg, false_reg, uval, uval32, opcode, is_jmp32);
-}
-
/* Regs are known to be equal, so intersect their min/max/var_off */
static void __reg_combine_min_max(struct bpf_reg_state *src_reg,
struct bpf_reg_state *dst_reg)
@@ -14881,53 +14883,32 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
return -EFAULT;
other_branch_regs = other_branch->frame[other_branch->curframe]->regs;
- /* detect if we are comparing against a constant value so we can adjust
- * our min/max values for our dst register.
- * this is only legit if both are scalars (or pointers to the same
- * object, I suppose, see the PTR_MAYBE_NULL related if block below),
- * because otherwise the different base pointers mean the offsets aren't
- * comparable.
- */
if (BPF_SRC(insn->code) == BPF_X) {
- struct bpf_reg_state *src_reg = ®s[insn->src_reg];
+ reg_set_min_max(&other_branch_regs[insn->dst_reg],
+ &other_branch_regs[insn->src_reg],
+ dst_reg, src_reg, opcode, is_jmp32);
if (dst_reg->type == SCALAR_VALUE &&
- src_reg->type == SCALAR_VALUE) {
- if (tnum_is_const(src_reg->var_off) ||
- (is_jmp32 &&
- tnum_is_const(tnum_subreg(src_reg->var_off))))
- reg_set_min_max(&other_branch_regs[insn->dst_reg],
- dst_reg,
- src_reg->var_off.value,
- tnum_subreg(src_reg->var_off).value,
- opcode, is_jmp32);
- else if (tnum_is_const(dst_reg->var_off) ||
- (is_jmp32 &&
- tnum_is_const(tnum_subreg(dst_reg->var_off))))
- reg_set_min_max_inv(&other_branch_regs[insn->src_reg],
- src_reg,
- dst_reg->var_off.value,
- tnum_subreg(dst_reg->var_off).value,
- opcode, is_jmp32);
- else if (!is_jmp32 &&
- (opcode == BPF_JEQ || opcode == BPF_JNE))
- /* Comparing for equality, we can combine knowledge */
- reg_combine_min_max(&other_branch_regs[insn->src_reg],
- &other_branch_regs[insn->dst_reg],
- src_reg, dst_reg, opcode);
- if (src_reg->id &&
- !WARN_ON_ONCE(src_reg->id != other_branch_regs[insn->src_reg].id)) {
- find_equal_scalars(this_branch, src_reg);
- find_equal_scalars(other_branch, &other_branch_regs[insn->src_reg]);
- }
-
- }
- } else if (dst_reg->type == SCALAR_VALUE) {
+ src_reg->type == SCALAR_VALUE &&
+ !is_jmp32 && (opcode == BPF_JEQ || opcode == BPF_JNE)) {
+ /* Comparing for equality, we can combine knowledge */
+ reg_combine_min_max(&other_branch_regs[insn->src_reg],
+ &other_branch_regs[insn->dst_reg],
+ src_reg, dst_reg, opcode);
+ }
+ } else /* BPF_SRC(insn->code) == BPF_K */ {
reg_set_min_max(&other_branch_regs[insn->dst_reg],
- dst_reg, insn->imm, (u32)insn->imm,
- opcode, is_jmp32);
+ src_reg /* fake one */,
+ dst_reg, src_reg /* same fake one */,
+ opcode, is_jmp32);
}
+ if (BPF_SRC(insn->code) == BPF_X &&
+ src_reg->type == SCALAR_VALUE && src_reg->id &&
+ !WARN_ON_ONCE(src_reg->id != other_branch_regs[insn->src_reg].id)) {
+ find_equal_scalars(this_branch, src_reg);
+ find_equal_scalars(other_branch, &other_branch_regs[insn->src_reg]);
+ }
if (dst_reg->type == SCALAR_VALUE && dst_reg->id &&
!WARN_ON_ONCE(dst_reg->id != other_branch_regs[insn->dst_reg].id)) {
find_equal_scalars(this_branch, dst_reg);
--
2.34.1
next prev parent reply other threads:[~2023-11-02 3:38 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-02 3:37 [PATCH v6 bpf-next 00/17] BPF register bounds logic and testing improvements Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 01/17] selftests/bpf: fix RELEASE=1 build for tc_opts Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 02/17] selftests/bpf: satisfy compiler by having explicit return in btf test Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 03/17] bpf: derive smin/smax from umin/max bounds Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 04/17] bpf: derive smin32/smax32 from umin32/umax32 bounds Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 05/17] bpf: derive subreg bounds from full bounds when upper 32 bits are constant Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 06/17] bpf: add special smin32/smax32 derivation from 64-bit bounds Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 07/17] bpf: improve deduction of 64-bit bounds from 32-bit bounds Andrii Nakryiko
2023-11-02 14:39 ` Shung-Hsi Yu
2023-11-02 16:17 ` Andrii Nakryiko
2023-11-03 3:43 ` Shung-Hsi Yu
2023-11-02 3:37 ` [PATCH v6 bpf-next 08/17] bpf: try harder to deduce register bounds from different numeric domains Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 09/17] bpf: drop knowledge-losing __reg_combine_{32,64}_into_{64,32} logic Andrii Nakryiko
2023-11-02 15:14 ` Shung-Hsi Yu
2023-11-02 3:37 ` [PATCH v6 bpf-next 10/17] selftests/bpf: BPF register range bounds tester Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 11/17] bpf: rename is_branch_taken reg arguments to prepare for the second one Andrii Nakryiko
2023-11-02 15:15 ` Shung-Hsi Yu
2023-11-02 3:37 ` [PATCH v6 bpf-next 12/17] bpf: generalize is_branch_taken() to work with two registers Andrii Nakryiko
2023-11-02 15:19 ` Shung-Hsi Yu
2023-11-02 3:37 ` [PATCH v6 bpf-next 13/17] bpf: move is_branch_taken() down Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 14/17] bpf: generalize is_branch_taken to handle all conditional jumps in one place Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 15/17] bpf: unify 32-bit and 64-bit is_branch_taken logic Andrii Nakryiko
2023-11-02 3:37 ` [PATCH v6 bpf-next 16/17] bpf: prepare reg_set_min_max for second set of registers Andrii Nakryiko
2023-11-02 3:37 ` Andrii Nakryiko [this message]
2023-11-02 16:10 ` [PATCH v6 bpf-next 00/17] BPF register bounds logic and testing improvements patchwork-bot+netdevbpf
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