From: Daniel Borkmann daniel@iogearbox.net
commit ede95a63b5e84ddeea6b0c473b36ab8bfd8c6ce3 upstream.
Rick reported that the BPF JIT could potentially fill the entire module space with BPF programs from unprivileged users which would prevent later attempts to load normal kernel modules or privileged BPF programs, for example. If JIT was enabled but unsuccessful to generate the image, then before commit 290af86629b2 ("bpf: introduce BPF_JIT_ALWAYS_ON config") we would always fall back to the BPF interpreter. Nowadays in the case where the CONFIG_BPF_JIT_ALWAYS_ON could be set, then the load will abort with a failure since the BPF interpreter was compiled out.
Add a global limit and enforce it for unprivileged users such that in case of BPF interpreter compiled out we fail once the limit has been reached or we fall back to BPF interpreter earlier w/o using module mem if latter was compiled in. In a next step, fair share among unprivileged users can be resolved in particular for the case where we would fail hard once limit is reached.
Fixes: 290af86629b2 ("bpf: introduce BPF_JIT_ALWAYS_ON config") Fixes: 0a14842f5a3c ("net: filter: Just In Time compiler for x86-64") Co-Developed-by: Rick Edgecombe rick.p.edgecombe@intel.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Alexei Starovoitov ast@kernel.org Cc: Eric Dumazet eric.dumazet@gmail.com Cc: Jann Horn jannh@google.com Cc: Kees Cook keescook@chromium.org Cc: LKML linux-kernel@vger.kernel.org Signed-off-by: Alexei Starovoitov ast@kernel.org [bwh: Backported to 4.9: adjust context] Signed-off-by: Ben Hutchings ben.hutchings@codethink.co.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Documentation/sysctl/net.txt | 8 +++++++ include/linux/filter.h | 1 kernel/bpf/core.c | 49 ++++++++++++++++++++++++++++++++++++++++--- net/core/sysctl_net_core.c | 10 +++++++- 4 files changed, 63 insertions(+), 5 deletions(-)
--- a/Documentation/sysctl/net.txt +++ b/Documentation/sysctl/net.txt @@ -54,6 +54,14 @@ Values : 1 - enable JIT hardening for unprivileged users only 2 - enable JIT hardening for all users
+bpf_jit_limit +------------- + +This enforces a global limit for memory allocations to the BPF JIT +compiler in order to reject unprivileged JIT requests once it has +been surpassed. bpf_jit_limit contains the value of the global limit +in bytes. + dev_weight --------------
--- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -599,6 +599,7 @@ void bpf_warn_invalid_xdp_action(u32 act #ifdef CONFIG_BPF_JIT extern int bpf_jit_enable; extern int bpf_jit_harden; +extern int bpf_jit_limit;
typedef void (*bpf_jit_fill_hole_t)(void *area, unsigned int size);
--- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -208,9 +208,43 @@ struct bpf_prog *bpf_patch_insn_single(s }
#ifdef CONFIG_BPF_JIT +# define BPF_JIT_LIMIT_DEFAULT (PAGE_SIZE * 40000) + /* All BPF JIT sysctl knobs here. */ int bpf_jit_enable __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_ALWAYS_ON); int bpf_jit_harden __read_mostly; +int bpf_jit_limit __read_mostly = BPF_JIT_LIMIT_DEFAULT; + +static atomic_long_t bpf_jit_current; + +#if defined(MODULES_VADDR) +static int __init bpf_jit_charge_init(void) +{ + /* Only used as heuristic here to derive limit. */ + bpf_jit_limit = min_t(u64, round_up((MODULES_END - MODULES_VADDR) >> 2, + PAGE_SIZE), INT_MAX); + return 0; +} +pure_initcall(bpf_jit_charge_init); +#endif + +static int bpf_jit_charge_modmem(u32 pages) +{ + if (atomic_long_add_return(pages, &bpf_jit_current) > + (bpf_jit_limit >> PAGE_SHIFT)) { + if (!capable(CAP_SYS_ADMIN)) { + atomic_long_sub(pages, &bpf_jit_current); + return -EPERM; + } + } + + return 0; +} + +static void bpf_jit_uncharge_modmem(u32 pages) +{ + atomic_long_sub(pages, &bpf_jit_current); +}
struct bpf_binary_header * bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr, @@ -218,21 +252,27 @@ bpf_jit_binary_alloc(unsigned int progle bpf_jit_fill_hole_t bpf_fill_ill_insns) { struct bpf_binary_header *hdr; - unsigned int size, hole, start; + u32 size, hole, start, pages;
/* Most of BPF filters are really small, but if some of them * fill a page, allow at least 128 extra bytes to insert a * random section of illegal instructions. */ size = round_up(proglen + sizeof(*hdr) + 128, PAGE_SIZE); + pages = size / PAGE_SIZE; + + if (bpf_jit_charge_modmem(pages)) + return NULL; hdr = module_alloc(size); - if (hdr == NULL) + if (!hdr) { + bpf_jit_uncharge_modmem(pages); return NULL; + }
/* Fill space with illegal/arch-dep instructions. */ bpf_fill_ill_insns(hdr, size);
- hdr->pages = size / PAGE_SIZE; + hdr->pages = pages; hole = min_t(unsigned int, size - (proglen + sizeof(*hdr)), PAGE_SIZE - sizeof(*hdr)); start = (get_random_int() % hole) & ~(alignment - 1); @@ -245,7 +285,10 @@ bpf_jit_binary_alloc(unsigned int progle
void bpf_jit_binary_free(struct bpf_binary_header *hdr) { + u32 pages = hdr->pages; + module_memfree(hdr); + bpf_jit_uncharge_modmem(pages); }
static int bpf_jit_blind_insn(const struct bpf_insn *from, --- a/net/core/sysctl_net_core.c +++ b/net/core/sysctl_net_core.c @@ -253,7 +253,6 @@ static int proc_dointvec_minmax_bpf_enab return ret; }
-# ifdef CONFIG_HAVE_EBPF_JIT static int proc_dointvec_minmax_bpf_restricted(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, @@ -264,7 +263,6 @@ proc_dointvec_minmax_bpf_restricted(stru
return proc_dointvec_minmax(table, write, buffer, lenp, ppos); } -# endif #endif
static struct ctl_table net_core_table[] = { @@ -348,6 +346,14 @@ static struct ctl_table net_core_table[] .extra2 = &two, }, # endif + { + .procname = "bpf_jit_limit", + .data = &bpf_jit_limit, + .maxlen = sizeof(int), + .mode = 0600, + .proc_handler = proc_dointvec_minmax_bpf_restricted, + .extra1 = &one, + }, #endif { .procname = "netdev_tstamp_prequeue",