* [PATCH bpf-next v2 0/3] check bpf_func_state->callback_depth when pruning states @ 2024-02-16 15:03 Eduard Zingerman 2024-02-16 15:03 ` [PATCH bpf-next v2 1/3] selftests/bpf: update tcp_custom_syncookie to use scalar packet offset Eduard Zingerman ` (2 more replies) 0 siblings, 3 replies; 9+ messages in thread From: Eduard Zingerman @ 2024-02-16 15:03 UTC (permalink / raw) To: bpf, ast Cc: andrii, daniel, martin.lau, kernel-team, yonghong.song, kuniyu, Eduard Zingerman This patch-set fixes bug in states pruning logic hit in mailing list discussion [0]. The details of the fix are in patch #2. A change to the test case test_tcp_custom_syncookie.c is necessary, otherwise updated verifier won't be able to process it due to instruction complexity limit. This change is done in patch #1. The main idea for the fix belongs to Yonghong Song, mine contribution is merely in review and test cases. There are some changes in verification performance: File Program Insns (DIFF) States (A) States (B) States (DIFF) ------------------------- -------- -------------- ---------- ---------- ------------- pyperf600_bpf_loop.bpf.o on_event +53 (+1.09%) 323 330 +7 (+2.17%) strobemeta_bpf_loop.bpf.o on_event +594 (+27.85%) 163 213 +50 (+30.67%) (when tested using BPF selftests and Cilium object files) Changelog: v1 [1] -> v2: - patch #2 commit message updated to better reflect verifier behavior with regards to checkpoints tree (suggested by Yonghong); - veristat results added (suggested by Andrii). [0] https://lore.kernel.org/bpf/9b251840-7cb8-4d17-bd23-1fc8071d8eef@linux.dev/ [1] https://lore.kernel.org/bpf/20240212143832.28838-1-eddyz87@gmail.com/ Eduard Zingerman (3): selftests/bpf: update tcp_custom_syncookie to use scalar packet offset bpf: check bpf_func_state->callback_depth when pruning states selftests/bpf: test case for callback_depth states pruning logic kernel/bpf/verifier.c | 3 + .../bpf/progs/test_tcp_custom_syncookie.c | 83 ++++++++++++------- .../bpf/progs/verifier_iterating_callbacks.c | 70 ++++++++++++++++ 3 files changed, 126 insertions(+), 30 deletions(-) -- 2.43.0 ^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH bpf-next v2 1/3] selftests/bpf: update tcp_custom_syncookie to use scalar packet offset 2024-02-16 15:03 [PATCH bpf-next v2 0/3] check bpf_func_state->callback_depth when pruning states Eduard Zingerman @ 2024-02-16 15:03 ` Eduard Zingerman 2024-02-16 15:03 ` [PATCH bpf-next v2 2/3] bpf: check bpf_func_state->callback_depth when pruning states Eduard Zingerman 2024-02-16 15:03 ` [PATCH bpf-next v2 3/3] selftests/bpf: test case for callback_depth states pruning logic Eduard Zingerman 2 siblings, 0 replies; 9+ messages in thread From: Eduard Zingerman @ 2024-02-16 15:03 UTC (permalink / raw) To: bpf, ast Cc: andrii, daniel, martin.lau, kernel-team, yonghong.song, kuniyu, Eduard Zingerman The next commit in a series fixes bug in bpf_loop() handling. That change makes tcp_custom_syncookie test too complex to verify. This commit updates tcp_custom_syncookie.c:tcp_parse_option() to use explicit packet offset (ctx->off) for packet access instead of ever moving pointer (ctx->ptr), this reduces verification complexity: - the tcp_parse_option() is passed as a callback to bpf_loop(); - suppose a checkpoint is created each time at function entry; - the ctx->ptr is tracked by verifier as PTR_TO_PACKET; - the ctx->ptr is incremented in tcp_parse_option(), thus umax_value field tracked for it is incremented as well; - on each next iteration of tcp_parse_option() checkpoint from a previous iteration can't be reused for state pruning, because PTR_TO_PACKET registers are considered equivalent only if old->umax_value >= cur->umax_value; - on the other hand, the ctx->off is a SCALAR, subject to widen_imprecise_scalars(); - it's exact bounds are eventually forgotten and it is tracked as unknown scalar at entry to tcp_parse_option(); - hence checkpoints created at the start of the function eventually converge. The change is similar to one applied in [0] to xdp_synproxy_kern.c. [0] commit 977bc146d4eb ("selftests/bpf: track tcp payload offset as scalar in xdp_synproxy") Acked-by: Yonghong Song <yonghong.song@linux.dev> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> --- .../bpf/progs/test_tcp_custom_syncookie.c | 83 ++++++++++++------- 1 file changed, 53 insertions(+), 30 deletions(-) diff --git a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c index a5501b29979a..c8e4553648bf 100644 --- a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c +++ b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c @@ -10,6 +10,8 @@ #include "test_siphash.h" #include "test_tcp_custom_syncookie.h" +#define MAX_PACKET_OFF 0xffff + /* Hash is calculated for each client and split into ISN and TS. * * MSB LSB @@ -52,16 +54,15 @@ static siphash_key_t test_key_siphash = { struct tcp_syncookie { struct __sk_buff *skb; + void *data; void *data_end; struct ethhdr *eth; struct iphdr *ipv4; struct ipv6hdr *ipv6; struct tcphdr *tcp; - union { - char *ptr; - __be32 *ptr32; - }; + __be32 *ptr32; struct bpf_tcp_req_attrs attrs; + u32 off; u32 cookie; u64 first; }; @@ -70,6 +71,7 @@ bool handled_syn, handled_ack; static int tcp_load_headers(struct tcp_syncookie *ctx) { + ctx->data = (void *)(long)ctx->skb->data; ctx->data_end = (void *)(long)ctx->skb->data_end; ctx->eth = (struct ethhdr *)(long)ctx->skb->data; @@ -134,6 +136,7 @@ static int tcp_reload_headers(struct tcp_syncookie *ctx) if (bpf_skb_change_tail(ctx->skb, data_len + 60 - ctx->tcp->doff * 4, 0)) goto err; + ctx->data = (void *)(long)ctx->skb->data; ctx->data_end = (void *)(long)ctx->skb->data_end; ctx->eth = (struct ethhdr *)(long)ctx->skb->data; if (ctx->ipv4) { @@ -195,47 +198,68 @@ static int tcp_validate_header(struct tcp_syncookie *ctx) return -1; } -static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx) +static __always_inline void *next(struct tcp_syncookie *ctx, __u32 sz) { - char opcode, opsize; + __u64 off = ctx->off; + __u8 *data; - if (ctx->ptr + 1 > ctx->data_end) - goto stop; + /* Verifier forbids access to packet when offset exceeds MAX_PACKET_OFF */ + if (off > MAX_PACKET_OFF - sz) + return NULL; + + data = ctx->data + off; + barrier_var(data); + if (data + sz >= ctx->data_end) + return NULL; - opcode = *ctx->ptr++; + ctx->off += sz; + return data; +} - if (opcode == TCPOPT_EOL) +static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx) +{ + __u8 *opcode, *opsize, *wscale; + __u32 *tsval, *tsecr; + __u16 *mss; + __u32 off; + + off = ctx->off; + opcode = next(ctx, 1); + if (!opcode) goto stop; - if (opcode == TCPOPT_NOP) + if (*opcode == TCPOPT_EOL) + goto stop; + + if (*opcode == TCPOPT_NOP) goto next; - if (ctx->ptr + 1 > ctx->data_end) + opsize = next(ctx, 1); + if (!opsize) goto stop; - opsize = *ctx->ptr++; - - if (opsize < 2) + if (*opsize < 2) goto stop; - switch (opcode) { + switch (*opcode) { case TCPOPT_MSS: - if (opsize == TCPOLEN_MSS && ctx->tcp->syn && - ctx->ptr + (TCPOLEN_MSS - 2) < ctx->data_end) - ctx->attrs.mss = get_unaligned_be16(ctx->ptr); + mss = next(ctx, 2); + if (*opsize == TCPOLEN_MSS && ctx->tcp->syn && mss) + ctx->attrs.mss = get_unaligned_be16(mss); break; case TCPOPT_WINDOW: - if (opsize == TCPOLEN_WINDOW && ctx->tcp->syn && - ctx->ptr + (TCPOLEN_WINDOW - 2) < ctx->data_end) { + wscale = next(ctx, 1); + if (*opsize == TCPOLEN_WINDOW && ctx->tcp->syn && wscale) { ctx->attrs.wscale_ok = 1; - ctx->attrs.snd_wscale = *ctx->ptr; + ctx->attrs.snd_wscale = *wscale; } break; case TCPOPT_TIMESTAMP: - if (opsize == TCPOLEN_TIMESTAMP && - ctx->ptr + (TCPOLEN_TIMESTAMP - 2) < ctx->data_end) { - ctx->attrs.rcv_tsval = get_unaligned_be32(ctx->ptr); - ctx->attrs.rcv_tsecr = get_unaligned_be32(ctx->ptr + 4); + tsval = next(ctx, 4); + tsecr = next(ctx, 4); + if (*opsize == TCPOLEN_TIMESTAMP && tsval && tsecr) { + ctx->attrs.rcv_tsval = get_unaligned_be32(tsval); + ctx->attrs.rcv_tsecr = get_unaligned_be32(tsecr); if (ctx->tcp->syn && ctx->attrs.rcv_tsecr) ctx->attrs.tstamp_ok = 0; @@ -244,13 +268,12 @@ static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx) } break; case TCPOPT_SACK_PERM: - if (opsize == TCPOLEN_SACK_PERM && ctx->tcp->syn && - ctx->ptr + (TCPOLEN_SACK_PERM - 2) < ctx->data_end) + if (*opsize == TCPOLEN_SACK_PERM && ctx->tcp->syn) ctx->attrs.sack_ok = 1; break; } - ctx->ptr += opsize - 2; + ctx->off = off + *opsize; next: return 0; stop: @@ -259,7 +282,7 @@ static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx) static void tcp_parse_options(struct tcp_syncookie *ctx) { - ctx->ptr = (char *)(ctx->tcp + 1); + ctx->off = (__u8 *)(ctx->tcp + 1) - (__u8 *)ctx->data, bpf_loop(40, tcp_parse_option, ctx, 0); } -- 2.43.0 ^ permalink raw reply related [flat|nested] 9+ messages in thread
* [PATCH bpf-next v2 2/3] bpf: check bpf_func_state->callback_depth when pruning states 2024-02-16 15:03 [PATCH bpf-next v2 0/3] check bpf_func_state->callback_depth when pruning states Eduard Zingerman 2024-02-16 15:03 ` [PATCH bpf-next v2 1/3] selftests/bpf: update tcp_custom_syncookie to use scalar packet offset Eduard Zingerman @ 2024-02-16 15:03 ` Eduard Zingerman 2024-02-16 18:16 ` Andrii Nakryiko 2024-02-16 15:03 ` [PATCH bpf-next v2 3/3] selftests/bpf: test case for callback_depth states pruning logic Eduard Zingerman 2 siblings, 1 reply; 9+ messages in thread From: Eduard Zingerman @ 2024-02-16 15:03 UTC (permalink / raw) To: bpf, ast Cc: andrii, daniel, martin.lau, kernel-team, yonghong.song, kuniyu, Eduard Zingerman When comparing current and cached states verifier should consider bpf_func_state->callback_depth. Current state cannot be pruned against cached state, when current states has more iterations left compared to cached state. Current state has more iterations left when it's callback_depth is smaller. Below is an example illustrating this bug, minimized from mailing list discussion [0]. The example is not a safe program: if loop_cb point (1) is followed by loop_cb point (2), then division by zero is possible at point (4). struct ctx { __u64 a; __u64 b; __u64 c; }; static void loop_cb(int i, struct ctx *ctx) { /* assume that generated code is "fallthrough-first": * if ... == 1 goto * if ... == 2 goto * <default> */ switch (bpf_get_prandom_u32()) { case 1: /* 1 */ ctx->a = 42; return 0; break; case 2: /* 2 */ ctx->b = 42; return 0; break; default: /* 3 */ ctx->c = 42; return 0; break; } } SEC("tc") __failure __flag(BPF_F_TEST_STATE_FREQ) int test(struct __sk_buff *skb) { struct ctx ctx = { 7, 7, 7 }; bpf_loop(2, loop_cb, &ctx, 0); /* 0 */ /* assume generated checks are in-order: .a first */ if (ctx.a == 42 && ctx.b == 42 && ctx.c == 7) asm volatile("r0 /= 0;":::"r0"); /* 4 */ return 0; } Prior to this commit verifier built the following checkpoint tree for this example: .------------------------------------- Checkpoint / State name | .-------------------------------- Code point number | | .---------------------------- Stack state {ctx.a,ctx.b,ctx.c} | | | .------------------- Callback depth in frame #0 v v v v - (0) {7P,7P,7},depth=0 - (3) {7P,7P,7},depth=1 - (0) {7P,7P,42},depth=1 - (3) {7P,7,42},depth=2 - (0) {7P,7,42},depth=2 loop terminates because of depth limit - (4) {7P,7,42},depth=0 predicted false, ctx.a marked precise - (6) exit - (2) {7P,7,42},depth=2 (a) - (0) {7P,42,42},depth=2 loop terminates because of depth limit - (4) {7P,42,42},depth=0 predicted false, ctx.a marked precise - (6) exit (b) - (1) {7P,7P,42},depth=2 - (0) {42P,7P,42},depth=2 loop terminates because of depth limit - (4) {42P,7P,42},depth=0 predicted false, ctx.{a,b} marked precise - (6) exit - (2) {7P,7,7},depth=1 - (0) {7P,42,7},depth=1 considered safe, pruned using checkpoint (a) (c) - (1) {7P,7P,7},depth=1 considered safe, pruned using checkpoint (b) Here checkpoint (b) has callback_depth of 2, meaning that it would never reach state {42,42,7}. While checkpoint (c) has callback_depth of 1, and thus could yet explore the state {42,42,7} if not pruned prematurely. This commit makes forbids such premature pruning, allowing verifier to explore states sub-tree starting at (c): (c) - (1) {7,7,7P},depth=1 - (0) {42P,7,7P},depth=1 ... - (2) {42,7,7},depth=2 - (0) {42,42,7},depth=2 loop terminates because of depth limit - (4) {42,42,7},depth=0 predicted true, ctx.{a,b,c} marked precise - (5) division by zero [0] https://lore.kernel.org/bpf/9b251840-7cb8-4d17-bd23-1fc8071d8eef@linux.dev/ Suggested-by: Yonghong Song <yonghong.song@linux.dev> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> --- kernel/bpf/verifier.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 011d54a1dc53..c1fa1de590dc 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16705,6 +16705,9 @@ static bool func_states_equal(struct bpf_verifier_env *env, struct bpf_func_stat { int i; + if (old->callback_depth > cur->callback_depth) + return false; + for (i = 0; i < MAX_BPF_REG; i++) if (!regsafe(env, &old->regs[i], &cur->regs[i], &env->idmap_scratch, exact)) -- 2.43.0 ^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH bpf-next v2 2/3] bpf: check bpf_func_state->callback_depth when pruning states 2024-02-16 15:03 ` [PATCH bpf-next v2 2/3] bpf: check bpf_func_state->callback_depth when pruning states Eduard Zingerman @ 2024-02-16 18:16 ` Andrii Nakryiko 2024-02-17 18:19 ` Eduard Zingerman 0 siblings, 1 reply; 9+ messages in thread From: Andrii Nakryiko @ 2024-02-16 18:16 UTC (permalink / raw) To: Eduard Zingerman Cc: bpf, ast, andrii, daniel, martin.lau, kernel-team, yonghong.song, kuniyu On Fri, Feb 16, 2024 at 7:03 AM Eduard Zingerman <eddyz87@gmail.com> wrote: > > When comparing current and cached states verifier should consider > bpf_func_state->callback_depth. Current state cannot be pruned against > cached state, when current states has more iterations left compared to > cached state. Current state has more iterations left when it's > callback_depth is smaller. > > Below is an example illustrating this bug, minimized from mailing list > discussion [0]. > The example is not a safe program: if loop_cb point (1) is followed by > loop_cb point (2), then division by zero is possible at point (4). > > struct ctx { > __u64 a; > __u64 b; > __u64 c; > }; > > static void loop_cb(int i, struct ctx *ctx) > { > /* assume that generated code is "fallthrough-first": > * if ... == 1 goto > * if ... == 2 goto > * <default> > */ > switch (bpf_get_prandom_u32()) { > case 1: /* 1 */ ctx->a = 42; return 0; break; > case 2: /* 2 */ ctx->b = 42; return 0; break; > default: /* 3 */ ctx->c = 42; return 0; break; > } > } > > SEC("tc") > __failure > __flag(BPF_F_TEST_STATE_FREQ) > int test(struct __sk_buff *skb) > { > struct ctx ctx = { 7, 7, 7 }; > > bpf_loop(2, loop_cb, &ctx, 0); /* 0 */ > /* assume generated checks are in-order: .a first */ > if (ctx.a == 42 && ctx.b == 42 && ctx.c == 7) > asm volatile("r0 /= 0;":::"r0"); /* 4 */ > return 0; > } > > Prior to this commit verifier built the following checkpoint tree for > this example: > > .------------------------------------- Checkpoint / State name > | .-------------------------------- Code point number > | | .---------------------------- Stack state {ctx.a,ctx.b,ctx.c} > | | | .------------------- Callback depth in frame #0 > v v v v > - (0) {7P,7P,7},depth=0 > - (3) {7P,7P,7},depth=1 > - (0) {7P,7P,42},depth=1 > - (3) {7P,7,42},depth=2 > - (0) {7P,7,42},depth=2 loop terminates because of depth limit > - (4) {7P,7,42},depth=0 predicted false, ctx.a marked precise > - (6) exit > - (2) {7P,7,42},depth=2 > (a) - (0) {7P,42,42},depth=2 loop terminates because of depth limit > - (4) {7P,42,42},depth=0 predicted false, ctx.a marked precise > - (6) exit > (b) - (1) {7P,7P,42},depth=2 > - (0) {42P,7P,42},depth=2 loop terminates because of depth limit > - (4) {42P,7P,42},depth=0 predicted false, ctx.{a,b} marked precise > - (6) exit > - (2) {7P,7,7},depth=1 > - (0) {7P,42,7},depth=1 considered safe, pruned using checkpoint (a) > (c) - (1) {7P,7P,7},depth=1 considered safe, pruned using checkpoint (b) > > Here checkpoint (b) has callback_depth of 2, meaning that it would > never reach state {42,42,7}. > While checkpoint (c) has callback_depth of 1, and thus > could yet explore the state {42,42,7} if not pruned prematurely. > This commit makes forbids such premature pruning, > allowing verifier to explore states sub-tree starting at (c): > > (c) - (1) {7,7,7P},depth=1 > - (0) {42P,7,7P},depth=1 > ... > - (2) {42,7,7},depth=2 > - (0) {42,42,7},depth=2 loop terminates because of depth limit > - (4) {42,42,7},depth=0 predicted true, ctx.{a,b,c} marked precise > - (5) division by zero > > [0] https://lore.kernel.org/bpf/9b251840-7cb8-4d17-bd23-1fc8071d8eef@linux.dev/ > > Suggested-by: Yonghong Song <yonghong.song@linux.dev> > Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> > --- > kernel/bpf/verifier.c | 3 +++ > 1 file changed, 3 insertions(+) > Missing Fixes: tag? Also, shouldn't this go into bpf tree instead of bpf-next? Otherwise everything looks good. > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 011d54a1dc53..c1fa1de590dc 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -16705,6 +16705,9 @@ static bool func_states_equal(struct bpf_verifier_env *env, struct bpf_func_stat > { > int i; > > + if (old->callback_depth > cur->callback_depth) > + return false; > + > for (i = 0; i < MAX_BPF_REG; i++) > if (!regsafe(env, &old->regs[i], &cur->regs[i], > &env->idmap_scratch, exact)) > -- > 2.43.0 > ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH bpf-next v2 2/3] bpf: check bpf_func_state->callback_depth when pruning states 2024-02-16 18:16 ` Andrii Nakryiko @ 2024-02-17 18:19 ` Eduard Zingerman 2024-02-19 12:48 ` Eduard Zingerman 0 siblings, 1 reply; 9+ messages in thread From: Eduard Zingerman @ 2024-02-17 18:19 UTC (permalink / raw) To: Andrii Nakryiko Cc: bpf, ast, andrii, daniel, martin.lau, kernel-team, yonghong.song, kuniyu On Fri, 2024-02-16 at 10:16 -0800, Andrii Nakryiko wrote: [...] > Missing Fixes: tag? Right, sorry aboutt that > Also, shouldn't this go into bpf tree instead of bpf-next? Will re-send v3 with fixes tag to 'bpf' ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH bpf-next v2 2/3] bpf: check bpf_func_state->callback_depth when pruning states 2024-02-17 18:19 ` Eduard Zingerman @ 2024-02-19 12:48 ` Eduard Zingerman 2024-02-20 0:30 ` Yonghong Song 0 siblings, 1 reply; 9+ messages in thread From: Eduard Zingerman @ 2024-02-19 12:48 UTC (permalink / raw) To: Andrii Nakryiko Cc: bpf, ast, andrii, daniel, martin.lau, kernel-team, yonghong.song, kuniyu On Sat, 2024-02-17 at 20:19 +0200, Eduard Zingerman wrote: [...] > > Also, shouldn't this go into bpf tree instead of bpf-next? > > Will re-send v3 with fixes tag to 'bpf' Sending via 'bpf' tree would require dropping patch #1. The test_tcp_custom_syncookie is not yet in 'bpf'. Note that patch #2 breaks syncookie test w/o patch #1. Should I split this in two parts? - patch #1 - send via bpf-next - patch #2,3 - send via bpf ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH bpf-next v2 2/3] bpf: check bpf_func_state->callback_depth when pruning states 2024-02-19 12:48 ` Eduard Zingerman @ 2024-02-20 0:30 ` Yonghong Song 0 siblings, 0 replies; 9+ messages in thread From: Yonghong Song @ 2024-02-20 0:30 UTC (permalink / raw) To: Eduard Zingerman, Andrii Nakryiko Cc: bpf, ast, andrii, daniel, martin.lau, kernel-team, kuniyu On 2/19/24 4:48 AM, Eduard Zingerman wrote: > On Sat, 2024-02-17 at 20:19 +0200, Eduard Zingerman wrote: > [...] > >>> Also, shouldn't this go into bpf tree instead of bpf-next? >> Will re-send v3 with fixes tag to 'bpf' > Sending via 'bpf' tree would require dropping patch #1. > The test_tcp_custom_syncookie is not yet in 'bpf'. > Note that patch #2 breaks syncookie test w/o patch #1. > Should I split this in two parts? > - patch #1 - send via bpf-next > - patch #2,3 - send via bpf Sounds good to me. Patch 1 will likely to be merged in bpf-next before patch 2/3 merged in bpf tree and circulared back to bpf-next. Please add related commit message in Patch 1 to explain actual fix will go to bpf tree and will be back to bpf-next later. ^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH bpf-next v2 3/3] selftests/bpf: test case for callback_depth states pruning logic 2024-02-16 15:03 [PATCH bpf-next v2 0/3] check bpf_func_state->callback_depth when pruning states Eduard Zingerman 2024-02-16 15:03 ` [PATCH bpf-next v2 1/3] selftests/bpf: update tcp_custom_syncookie to use scalar packet offset Eduard Zingerman 2024-02-16 15:03 ` [PATCH bpf-next v2 2/3] bpf: check bpf_func_state->callback_depth when pruning states Eduard Zingerman @ 2024-02-16 15:03 ` Eduard Zingerman 2024-02-20 0:32 ` Yonghong Song 2 siblings, 1 reply; 9+ messages in thread From: Eduard Zingerman @ 2024-02-16 15:03 UTC (permalink / raw) To: bpf, ast Cc: andrii, daniel, martin.lau, kernel-team, yonghong.song, kuniyu, Eduard Zingerman The test case was minimized from mailing list discussion [0]. It is equivalent to the following C program: struct iter_limit_bug_ctx { __u64 a; __u64 b; __u64 c; }; static __naked void iter_limit_bug_cb(void) { switch (bpf_get_prandom_u32()) { case 1: ctx->a = 42; break; case 2: ctx->b = 42; break; default: ctx->c = 42; break; } } int iter_limit_bug(struct __sk_buff *skb) { struct iter_limit_bug_ctx ctx = { 7, 7, 7 }; bpf_loop(2, iter_limit_bug_cb, &ctx, 0); if (ctx.a == 42 && ctx.b == 42 && ctx.c == 7) asm volatile("r1 /= 0;":::"r1"); return 0; } The main idea is that each loop iteration changes one of the state variables in a non-deterministic manner. Hence it is premature to prune the states that have two iterations left comparing them to states with one iteration left. E.g. {{7,7,7}, callback_depth=0} can reach state {42,42,7}, while {{7,7,7}, callback_depth=1} can't. [0] https://lore.kernel.org/bpf/9b251840-7cb8-4d17-bd23-1fc8071d8eef@linux.dev/ Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> --- .../bpf/progs/verifier_iterating_callbacks.c | 70 +++++++++++++++++++ 1 file changed, 70 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/verifier_iterating_callbacks.c b/tools/testing/selftests/bpf/progs/verifier_iterating_callbacks.c index 5905e036e0ea..a955a6358206 100644 --- a/tools/testing/selftests/bpf/progs/verifier_iterating_callbacks.c +++ b/tools/testing/selftests/bpf/progs/verifier_iterating_callbacks.c @@ -239,4 +239,74 @@ int bpf_loop_iter_limit_nested(void *unused) return 1000 * a + b + c; } +struct iter_limit_bug_ctx { + __u64 a; + __u64 b; + __u64 c; +}; + +static __naked void iter_limit_bug_cb(void) +{ + /* This is the same as C code below, but written + * in assembly to control which branches are fall-through. + * + * switch (bpf_get_prandom_u32()) { + * case 1: ctx->a = 42; break; + * case 2: ctx->b = 42; break; + * default: ctx->c = 42; break; + * } + */ + asm volatile ( + "r9 = r2;" + "call %[bpf_get_prandom_u32];" + "r1 = r0;" + "r2 = 42;" + "r0 = 0;" + "if r1 == 0x1 goto 1f;" + "if r1 == 0x2 goto 2f;" + "*(u64 *)(r9 + 16) = r2;" + "exit;" + "1: *(u64 *)(r9 + 0) = r2;" + "exit;" + "2: *(u64 *)(r9 + 8) = r2;" + "exit;" + : + : __imm(bpf_get_prandom_u32) + : __clobber_all + ); +} + +SEC("tc") +__failure +__flag(BPF_F_TEST_STATE_FREQ) +int iter_limit_bug(struct __sk_buff *skb) +{ + struct iter_limit_bug_ctx ctx = { 7, 7, 7 }; + + bpf_loop(2, iter_limit_bug_cb, &ctx, 0); + + /* This is the same as C code below, + * written in assembly to guarantee checks order. + * + * if (ctx.a == 42 && ctx.b == 42 && ctx.c == 7) + * asm volatile("r1 /= 0;":::"r1"); + */ + asm volatile ( + "r1 = *(u64 *)%[ctx_a];" + "if r1 != 42 goto 1f;" + "r1 = *(u64 *)%[ctx_b];" + "if r1 != 42 goto 1f;" + "r1 = *(u64 *)%[ctx_c];" + "if r1 != 7 goto 1f;" + "r1 /= 0;" + "1:" + : + : [ctx_a]"m"(ctx.a), + [ctx_b]"m"(ctx.b), + [ctx_c]"m"(ctx.c) + : "r1" + ); + return 0; +} + char _license[] SEC("license") = "GPL"; -- 2.43.0 ^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH bpf-next v2 3/3] selftests/bpf: test case for callback_depth states pruning logic 2024-02-16 15:03 ` [PATCH bpf-next v2 3/3] selftests/bpf: test case for callback_depth states pruning logic Eduard Zingerman @ 2024-02-20 0:32 ` Yonghong Song 0 siblings, 0 replies; 9+ messages in thread From: Yonghong Song @ 2024-02-20 0:32 UTC (permalink / raw) To: Eduard Zingerman, bpf, ast Cc: andrii, daniel, martin.lau, kernel-team, kuniyu On 2/16/24 7:03 AM, Eduard Zingerman wrote: > The test case was minimized from mailing list discussion [0]. > It is equivalent to the following C program: > > struct iter_limit_bug_ctx { __u64 a; __u64 b; __u64 c; }; > > static __naked void iter_limit_bug_cb(void) > { > switch (bpf_get_prandom_u32()) { > case 1: ctx->a = 42; break; > case 2: ctx->b = 42; break; > default: ctx->c = 42; break; > } > } > > int iter_limit_bug(struct __sk_buff *skb) > { > struct iter_limit_bug_ctx ctx = { 7, 7, 7 }; > > bpf_loop(2, iter_limit_bug_cb, &ctx, 0); > if (ctx.a == 42 && ctx.b == 42 && ctx.c == 7) > asm volatile("r1 /= 0;":::"r1"); > return 0; > } > > The main idea is that each loop iteration changes one of the state > variables in a non-deterministic manner. Hence it is premature to > prune the states that have two iterations left comparing them to > states with one iteration left. > E.g. {{7,7,7}, callback_depth=0} can reach state {42,42,7}, > while {{7,7,7}, callback_depth=1} can't. > > [0] https://lore.kernel.org/bpf/9b251840-7cb8-4d17-bd23-1fc8071d8eef@linux.dev/ > > Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> Acked-by: Yonghong Song <yonghong.song@linux.dev> ^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2024-02-20 0:32 UTC | newest] Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2024-02-16 15:03 [PATCH bpf-next v2 0/3] check bpf_func_state->callback_depth when pruning states Eduard Zingerman 2024-02-16 15:03 ` [PATCH bpf-next v2 1/3] selftests/bpf: update tcp_custom_syncookie to use scalar packet offset Eduard Zingerman 2024-02-16 15:03 ` [PATCH bpf-next v2 2/3] bpf: check bpf_func_state->callback_depth when pruning states Eduard Zingerman 2024-02-16 18:16 ` Andrii Nakryiko 2024-02-17 18:19 ` Eduard Zingerman 2024-02-19 12:48 ` Eduard Zingerman 2024-02-20 0:30 ` Yonghong Song 2024-02-16 15:03 ` [PATCH bpf-next v2 3/3] selftests/bpf: test case for callback_depth states pruning logic Eduard Zingerman 2024-02-20 0:32 ` Yonghong Song
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