Gh0st
/
linux
mirror of https://github.com/torvalds/linux.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

x86/bpf: Call branch history clearing sequence on exit 

Classic BPF programs have been identified as potential vectors for
intra-mode Branch Target Injection (BTI) attacks. Classic BPF programs can
be run by unprivileged users. They allow unprivileged code to execute
inside the kernel. Attackers can use unprivileged cBPF to craft branch
history in kernel mode that can influence the target of indirect branches.

Introduce a branch history buffer (BHB) clearing sequence during the JIT
compilation of classic BPF programs. The clearing sequence is the same as
is used in previous mitigations to protect syscalls. Since eBPF programs
already have their own mitigations in place, only insert the call on
classic programs that aren't run by privileged users.

Signed-off-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
This commit is contained in:
Daniel Sneddon 2025-05-05 14:35:12 -07:00 committed by Dave Hansen
parent 92a09c4746
commit d4e89d212d
1 changed files with 31 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
arch/x86/net/bpf_jit_comp.c
View File

@ -1502,6 +1502,30 @@ static void emit_priv_frame_ptr(u8 **pprog, void __percpu *priv_frame_ptr)
#define PRIV_STACK_GUARD_SZ 8
#define PRIV_STACK_GUARD_VAL 0xEB9F12345678eb9fULL
static int emit_spectre_bhb_barrier(u8 **pprog, u8 *ip,
struct bpf_prog *bpf_prog)
{
u8 *prog = *pprog;
u8 *func;
if (cpu_feature_enabled(X86_FEATURE_CLEAR_BHB_LOOP)) {
/* The clearing sequence clobbers eax and ecx. */
EMIT1(0x50); /* push rax */
EMIT1(0x51); /* push rcx */
ip += 2;
func = (u8 *)clear_bhb_loop;
ip += x86_call_depth_emit_accounting(&prog, func, ip);
if (emit_call(&prog, func, ip))
return -EINVAL;
EMIT1(0x59); /* pop rcx */
EMIT1(0x58); /* pop rax */
}
*pprog = prog;
return 0;
}
static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image,
int oldproglen, struct jit_context *ctx, bool jmp_padding)
{
@ -2544,6 +2568,13 @@ st: if (is_imm8(insn->off))
seen_exit = true;
/* Update cleanup_addr */
ctx->cleanup_addr = proglen;
if (bpf_prog_was_classic(bpf_prog) &&
!capable(CAP_SYS_ADMIN)) {
u8 *ip = image + addrs[i - 1];
if (emit_spectre_bhb_barrier(&prog, ip, bpf_prog))
return -EINVAL;
}
if (bpf_prog->aux->exception_boundary) {
pop_callee_regs(&prog, all_callee_regs_used);
pop_r12(&prog);