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bpf: Restrict JIT predictor flush to cBPF

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Currently predictor flush on memory reuse is done for all BPF JIT
allocations, but only cBPF programs can be loaded by an unprivileged user.
eBPF is privileged by default, and flushing predictors for all CPUs on
every eBPF reuse penalizes the common case for no security benefit.

eBPF allocations can be frequent on busy systems, only flush predictors
for cBPF programs. Trampoline and dispatcher allocations also skip the
flush as they are eBPF-only.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Pawan Gupta
2026-06-29 22:38:23 -07:00
committed by Daniel Borkmann
parent a3af84b0fa
commit 0bb99f2cfa
9 changed files with 25 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
kernel/bpf/core.c
View File

@@ -942,7 +942,7 @@ static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_ins
return NULL;
}
void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)
void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns, bool was_classic)
{
unsigned int nbits = BPF_PROG_SIZE_TO_NBITS(size);
struct bpf_prog_pack *pack;
@@ -957,7 +957,7 @@ void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)
* safe because cBPF programs (the unprivileged attack surface)
* are bounded well below a pack size.
*/
if (static_branch_unlikely(&bpf_pred_flush_enabled))
if (was_classic && static_branch_unlikely(&bpf_pred_flush_enabled))
pr_warn_once("BPF: Predictors not flushed for allocations greater than BPF_PROG_PACK_SIZE\n");
size = round_up(size, PAGE_SIZE);
ptr = bpf_jit_alloc_exec(size);
@@ -989,7 +989,9 @@ void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)
pos = 0;
found_free_area:
static_call_cond(bpf_arch_pred_flush)();
/* Flush only for cBPF as it may contain a crafted gadget */
if (static_branch_unlikely(&bpf_pred_flush_enabled) && was_classic)
static_call_cond(bpf_arch_pred_flush)();
bitmap_set(pack->bitmap, pos, nbits);
ptr = (void *)(pack->ptr) + (pos << BPF_PROG_CHUNK_SHIFT);
@@ -1149,7 +1151,8 @@ bpf_jit_binary_pack_alloc(unsigned int proglen, u8 **image_ptr,
unsigned int alignment,
struct bpf_binary_header **rw_header,
u8 **rw_image,
bpf_jit_fill_hole_t bpf_fill_ill_insns)
bpf_jit_fill_hole_t bpf_fill_ill_insns,
bool was_classic)
{
struct bpf_binary_header *ro_header;
u32 size, hole, start;
@@ -1162,7 +1165,7 @@ bpf_jit_binary_pack_alloc(unsigned int proglen, u8 **image_ptr,
if (bpf_jit_charge_modmem(size))
return NULL;
ro_header = bpf_prog_pack_alloc(size, bpf_fill_ill_insns);
ro_header = bpf_prog_pack_alloc(size, bpf_fill_ill_insns, was_classic);
if (!ro_header) {
bpf_jit_uncharge_modmem(size);
return NULL;

2
kernel/bpf/dispatcher.c
View File

@@ -145,7 +145,7 @@ void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from,
mutex_lock(&d->mutex);
if (!d->image) {
d->image = bpf_prog_pack_alloc(PAGE_SIZE, bpf_jit_fill_hole_with_zero);
d->image = bpf_prog_pack_alloc(PAGE_SIZE, bpf_jit_fill_hole_with_zero, false);
if (!d->image)
goto out;
d->rw_image = bpf_jit_alloc_exec(PAGE_SIZE);