linux-stable.git/kernel/bpf/const_fold.c, branch v7.3-rc2

bpf: Introduce global percpu data

2026-08-13T17:27:40+00:00

Introduce global percpu data, inspired by the commit
6316f78306c1 ("Merge branch 'support-global-data'"). It enables the
definition of global percpu variables in BPF, similar to the
include/linux/percpu-defs.h::DEFINE_PER_CPU() macro.

For example, in BPF, it is able to define a global percpu variable like:

int data SEC(".percpu");

With this patch, tools like retsnoop [1] and bpfsnoop [2] can simplify
their BPF code for handling LBRs. The code can be updated from

static struct perf_branch_entry lbrs[1][MAX_LBR_ENTRIES] SEC(".data.lbrs");

to

static struct perf_branch_entry lbrs[MAX_LBR_ENTRIES] SEC(".percpu.lbrs");

This eliminates the need to retrieve the CPU ID using the
bpf_get_smp_processor_id() helper.

Additionally, by reusing global percpu data map, sharing information
between tail callers and callees or freplace callers and callees becomes
simpler compared to reusing percpu_array maps.

Links:
[1] https://github.com/anakryiko/retsnoop
[2] https://github.com/bpfsnoop/bpfsnoop

Signed-off-by: Leon Hwang 
Signed-off-by: Andrii Nakryiko 
Acked-by: Eduard Zingerman 
Link: https://lore.kernel.org/bpf/20260813152324.97937-4-leon.hwang@linux.dev

bpf: Derive the atomic load register in one place

2026-08-12T17:33:53+00:00

check_atomic_rmw() open codes the mapping from a BPF_ATOMIC to the register
it reads the old value into, the BPF_STX case of insn_def_regno() open codes
the very same mapping a second time, the const folding and the liveness
transfer functions a third and a fourth time, and BPF JITs need it as well
to know which register a faulting BPF_PROBE_ATOMIC has to clear.

Add a small helper so that all of them can share it. No functional change.
The BPF_LOAD_ACQ case is there for the JITs, which do walk all instruction
classes. const_reg_xfer() loses its explicit BPF_ATOMIC mode test since the
helper checks class and mode itself; the BPF_PROBE_ATOMIC it additionally
accepts cannot be seen there as it is only set from bpf_do_misc_fixups(),
that is, after const folding has run. arg_track_xfer() keeps its mode test
since that also guards the stack clearing next to it.

Signed-off-by: Daniel Borkmann 
Acked-by: Eduard Zingerman 
Link: https://patch.msgid.link/20260811131600.506721-1-daniel@iogearbox.net
Signed-off-by: Eduard Zingerman

bpf: Extend liveness analysis to track stack argument slots

2026-05-13T16:27:31+00:00

BPF_REG_PARAMS (R11) is at index MAX_BPF_REG, which is beyond the
register tracking arrays in const_fold.c and liveness.c. Handle it
explicitly to avoid out-of-bounds accesses.

Extend the arg tracking dataflow to cover stack arg slots. Otherwise,
pointers passed through stack args are invisible to liveness, causing
the pointed-to stack slots to be incorrectly poisoned.

Extend the at_out tracking array to MAX_AT_TRACK_REGS (registers
plus stack arg slots) so that outgoing stack arg stores are tracked
alongside registers. Add a separate at_stack_arg_entry array in
compute_subprog_args(), passed to arg_track_xfer(), to restore
FP-derived values on incoming stack arg reads.

Extend record_call_access() to check stack arg slots for FP-derived
pointers at kfunc call sites, reusing the record_arg_access() helper
extracted in the previous patch. Pass stack arg state from caller to
callee in analyze_subprog() so that callees can track pointers received
through stack args, hence avoid poisoning.

Skip stack arg instructions in record_load_store_access(). Stack arg
STX uses dst_reg=BPF_REG_PARAMS (index 11), but at[11] is repurposed
to track the value stored in stack arg slot 0. Without the skip, if a
prior stack arg STX stored an FP-derived pointer (e.g., fp-64) into
slot 0, a subsequent stack arg STX would read that FP-derived value as
the base pointer and spuriously mark a regular stack slot (e.g., fp-72
from -64 + -8) as accessed in the liveness bitmap.

Extend arg_track_log() to log state transitions for outgoing stack arg
slots at indices MAX_BPF_REG through MAX_AT_TRACK_REGS-1. Without this,
changes to at_out[11..17] caused by stack arg store instructions are
silently omitted from BPF_LOG_LEVEL2 output. For example, when a
caller passes fp-64 through a stack argument:

  subprog#0:
   10: (bf) r6 = r10
   11: (07) r6 += -64
   12: (7b) *(u64 *)(r11 -8) = r6
	sa0: none -> fp0-64
   13: (85) call pc+5

Without the fix, the "sa0: none -> fp0-64" transition at insn 12
would not appear.

Extend print_subprog_arg_access() to include stack arg slots in the
per-instruction FP-derived state dump. For example:

  subprog#0:
   12: (7b) *(u64 *)(r11 - 8) = r6  // r6=fp0-64
   13: (85) call pc+5              // r6=fp0-64 sa0=fp0-64

Without the fix, the "sa0=fp0-64" annotation at insn 13 would not
appear, making it harder to debug liveness analysis for programs
that pass FP-derived pointers through stack arguments.

Extend has_fp_args() to also check stack arg slots for FP-derived
pointers, so that callees receiving pointers only through stack args
are still recursively analyzed.

Signed-off-by: Yonghong Song 
Link: https://lore.kernel.org/r/20260513045043.2389049-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov

bpf: Add bpf_compute_const_regs() and bpf_prune_dead_branches() passes

2026-04-03T15:34:36+00:00

Add two passes before the main verifier pass:

bpf_compute_const_regs() is a forward dataflow analysis that tracks
register values in R0-R9 across the program using fixed-point
iteration in reverse postorder. Each register is tracked with
a six-state lattice:

  UNVISITED -> CONST(val) / MAP_PTR(map_index) /
               MAP_VALUE(map_index, offset) / SUBPROG(num) -> UNKNOWN

At merge points, if two paths produce the same state and value for
a register, it stays; otherwise it becomes UNKNOWN.

The analysis handles:
 - MOV, ADD, SUB, AND with immediate or register operands
 - LD_IMM64 for plain constants, map FDs, map values, and subprogs
 - LDX from read-only maps: constant-folds the load by reading the
   map value directly via bpf_map_direct_read()

Results that fit in 32 bits are stored per-instruction in
insn_aux_data and bitmasks.

bpf_prune_dead_branches() uses the computed constants to evaluate
conditional branches. When both operands of a conditional jump are
known constants, the branch outcome is determined statically and the
instruction is rewritten to an unconditional jump.
The CFG postorder is then recomputed to reflect new control flow.
This eliminates dead edges so that subsequent liveness analysis
doesn't propagate through dead code.

Also add runtime sanity check to validate that precomputed
constants match the verifier's tracked state.

Acked-by: Eduard Zingerman 
Link: https://lore.kernel.org/r/20260403024422.87231-5-alexei.starovoitov@gmail.com
Signed-off-by: Alexei Starovoitov