Commit 02088d9b authored by Russell King's avatar Russell King
Browse files

ARM: net: bpf: fix register saving

When an eBPF program tail-calls another eBPF program, it enters it after
the prologue to avoid having complex stack manipulations.  This can lead
to kernel oopses, and similar.

Resolve this by always using a fixed stack layout, a CPU register frame
pointer, and using this when reloading registers before returning.

Fixes: 39c13c20

 ("arm: eBPF JIT compiler")
Signed-off-by: default avatarRussell King <rmk+kernel@armlinux.org.uk>
parent 0005e55a
......@@ -61,20 +61,24 @@ int bpf_jit_enable __read_mostly;
*
* high
* original ARM_SP => +------------------+
* | lr | (optional)
* | r4-r8,r10 | callee saved registers
* +------------------+
* | r4-r8,r10,fp,lr | callee saved registers
* current ARM_FP => +------------------+
* low
*
* When popping registers off the stack at the end of a BPF function, we
* reference them via the current ARM_FP register.
*/
#define CALLEE_MASK (1 << ARM_R4 | 1 << ARM_R5 | 1 << ARM_R6 | \
1 << ARM_R7 | 1 << ARM_R8 | 1 << ARM_R10 | \
1 << ARM_FP)
#define CALLEE_PUSH_MASK (CALLEE_MASK | 1 << ARM_LR)
#define CALLEE_POP_MASK (CALLEE_MASK | 1 << ARM_PC)
#define STACK_OFFSET(k) (k)
#define TMP_REG_1 (MAX_BPF_JIT_REG + 0) /* TEMP Register 1 */
#define TMP_REG_2 (MAX_BPF_JIT_REG + 1) /* TEMP Register 2 */
#define TCALL_CNT (MAX_BPF_JIT_REG + 2) /* Tail Call Count */
/* Flags used for JIT optimization */
#define SEEN_CALL (1 << 0)
#define FLAG_IMM_OVERFLOW (1 << 0)
/*
......@@ -135,7 +139,6 @@ static const u8 bpf2a32[][2] = {
* idx : index of current last JITed instruction.
* prologue_bytes : bytes used in prologue.
* epilogue_offset : offset of epilogue starting.
* seen : bit mask used for JIT optimization.
* offsets : array of eBPF instruction offsets in
* JITed code.
* target : final JITed code.
......@@ -150,7 +153,6 @@ struct jit_ctx {
unsigned int idx;
unsigned int prologue_bytes;
unsigned int epilogue_offset;
u32 seen;
u32 flags;
u32 *offsets;
u32 *target;
......@@ -340,7 +342,6 @@ static void emit_bx_r(u8 tgt_reg, struct jit_ctx *ctx)
static inline void emit_blx_r(u8 tgt_reg, struct jit_ctx *ctx)
{
ctx->seen |= SEEN_CALL;
#if __LINUX_ARM_ARCH__ < 5
emit(ARM_MOV_R(ARM_LR, ARM_PC), ctx);
emit_bx_r(tgt_reg, ctx);
......@@ -403,7 +404,6 @@ static inline void emit_udivmod(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx, u8 op)
}
/* Call appropriate function */
ctx->seen |= SEEN_CALL;
emit_mov_i(ARM_IP, op == BPF_DIV ?
(u32)jit_udiv32 : (u32)jit_mod32, ctx);
emit_blx_r(ARM_IP, ctx);
......@@ -669,8 +669,6 @@ static inline void emit_a32_lsh_r64(const u8 dst[], const u8 src[], bool dstk,
/* Do LSH operation */
emit(ARM_SUB_I(ARM_IP, rt, 32), ctx);
emit(ARM_RSB_I(tmp2[0], rt, 32), ctx);
/* As we are using ARM_LR */
ctx->seen |= SEEN_CALL;
emit(ARM_MOV_SR(ARM_LR, rm, SRTYPE_ASL, rt), ctx);
emit(ARM_ORR_SR(ARM_LR, ARM_LR, rd, SRTYPE_ASL, ARM_IP), ctx);
emit(ARM_ORR_SR(ARM_IP, ARM_LR, rd, SRTYPE_LSR, tmp2[0]), ctx);
......@@ -705,8 +703,6 @@ static inline void emit_a32_arsh_r64(const u8 dst[], const u8 src[], bool dstk,
/* Do the ARSH operation */
emit(ARM_RSB_I(ARM_IP, rt, 32), ctx);
emit(ARM_SUBS_I(tmp2[0], rt, 32), ctx);
/* As we are using ARM_LR */
ctx->seen |= SEEN_CALL;
emit(ARM_MOV_SR(ARM_LR, rd, SRTYPE_LSR, rt), ctx);
emit(ARM_ORR_SR(ARM_LR, ARM_LR, rm, SRTYPE_ASL, ARM_IP), ctx);
_emit(ARM_COND_MI, ARM_B(0), ctx);
......@@ -741,8 +737,6 @@ static inline void emit_a32_lsr_r64(const u8 dst[], const u8 src[], bool dstk,
/* Do LSH operation */
emit(ARM_RSB_I(ARM_IP, rt, 32), ctx);
emit(ARM_SUBS_I(tmp2[0], rt, 32), ctx);
/* As we are using ARM_LR */
ctx->seen |= SEEN_CALL;
emit(ARM_MOV_SR(ARM_LR, rd, SRTYPE_LSR, rt), ctx);
emit(ARM_ORR_SR(ARM_LR, ARM_LR, rm, SRTYPE_ASL, ARM_IP), ctx);
emit(ARM_ORR_SR(ARM_LR, ARM_LR, rm, SRTYPE_LSR, tmp2[0]), ctx);
......@@ -877,8 +871,6 @@ static inline void emit_a32_mul_r64(const u8 dst[], const u8 src[], bool dstk,
/* Do Multiplication */
emit(ARM_MUL(ARM_IP, rd, rn), ctx);
emit(ARM_MUL(ARM_LR, rm, rt), ctx);
/* As we are using ARM_LR */
ctx->seen |= SEEN_CALL;
emit(ARM_ADD_R(ARM_LR, ARM_IP, ARM_LR), ctx);
emit(ARM_UMULL(ARM_IP, rm, rd, rt), ctx);
......@@ -955,7 +947,6 @@ static inline void emit_ar_r(const u8 rd, const u8 rt, const u8 rm,
const u8 rn, struct jit_ctx *ctx, u8 op) {
switch (op) {
case BPF_JSET:
ctx->seen |= SEEN_CALL;
emit(ARM_AND_R(ARM_IP, rt, rn), ctx);
emit(ARM_AND_R(ARM_LR, rd, rm), ctx);
emit(ARM_ORRS_R(ARM_IP, ARM_LR, ARM_IP), ctx);
......@@ -1119,33 +1110,22 @@ static void build_prologue(struct jit_ctx *ctx)
const u8 r2 = bpf2a32[BPF_REG_1][1];
const u8 r3 = bpf2a32[BPF_REG_1][0];
const u8 r4 = bpf2a32[BPF_REG_6][1];
const u8 r5 = bpf2a32[BPF_REG_6][0];
const u8 r6 = bpf2a32[TMP_REG_1][1];
const u8 r7 = bpf2a32[TMP_REG_1][0];
const u8 r8 = bpf2a32[TMP_REG_2][1];
const u8 r10 = bpf2a32[TMP_REG_2][0];
const u8 fplo = bpf2a32[BPF_REG_FP][1];
const u8 fphi = bpf2a32[BPF_REG_FP][0];
const u8 sp = ARM_SP;
const u8 *tcc = bpf2a32[TCALL_CNT];
u16 reg_set = 0;
/* Save callee saved registers. */
reg_set |= (1<<r4) | (1<<r5) | (1<<r6) | (1<<r7) | (1<<r8) | (1<<r10);
#ifdef CONFIG_FRAME_POINTER
reg_set |= (1<<ARM_FP) | (1<<ARM_IP) | (1<<ARM_LR) | (1<<ARM_PC);
emit(ARM_MOV_R(ARM_IP, sp), ctx);
u16 reg_set = CALLEE_PUSH_MASK | 1 << ARM_IP | 1 << ARM_PC;
emit(ARM_MOV_R(ARM_IP, ARM_SP), ctx);
emit(ARM_PUSH(reg_set), ctx);
emit(ARM_SUB_I(ARM_FP, ARM_IP, 4), ctx);
#else
/* Check if call instruction exists in BPF body */
if (ctx->seen & SEEN_CALL)
reg_set |= (1<<ARM_LR);
emit(ARM_PUSH(reg_set), ctx);
emit(ARM_PUSH(CALLEE_PUSH_MASK), ctx);
emit(ARM_MOV_R(ARM_FP, ARM_SP), ctx);
#endif
/* Save frame pointer for later */
emit(ARM_SUB_I(ARM_IP, sp, SCRATCH_SIZE), ctx);
emit(ARM_SUB_I(ARM_IP, ARM_SP, SCRATCH_SIZE), ctx);
ctx->stack_size = imm8m(STACK_SIZE);
......@@ -1168,33 +1148,19 @@ static void build_prologue(struct jit_ctx *ctx)
/* end of prologue */
}
/* restore callee saved registers. */
static void build_epilogue(struct jit_ctx *ctx)
{
const u8 r4 = bpf2a32[BPF_REG_6][1];
const u8 r5 = bpf2a32[BPF_REG_6][0];
const u8 r6 = bpf2a32[TMP_REG_1][1];
const u8 r7 = bpf2a32[TMP_REG_1][0];
const u8 r8 = bpf2a32[TMP_REG_2][1];
const u8 r10 = bpf2a32[TMP_REG_2][0];
u16 reg_set = 0;
/* unwind function call stack */
emit(ARM_ADD_I(ARM_SP, ARM_SP, ctx->stack_size), ctx);
/* restore callee saved registers. */
reg_set |= (1<<r4) | (1<<r5) | (1<<r6) | (1<<r7) | (1<<r8) | (1<<r10);
#ifdef CONFIG_FRAME_POINTER
/* the first instruction of the prologue was: mov ip, sp */
reg_set |= (1<<ARM_FP) | (1<<ARM_SP) | (1<<ARM_PC);
/* When using frame pointers, some additional registers need to
* be loaded. */
u16 reg_set = CALLEE_POP_MASK | 1 << ARM_SP;
emit(ARM_SUB_I(ARM_SP, ARM_FP, hweight16(reg_set) * 4), ctx);
emit(ARM_LDM(ARM_SP, reg_set), ctx);
#else
if (ctx->seen & SEEN_CALL)
reg_set |= (1<<ARM_PC);
/* Restore callee saved registers. */
emit(ARM_POP(reg_set), ctx);
/* Return back to the callee function */
if (!(ctx->seen & SEEN_CALL))
emit_bx_r(ARM_LR, ctx);
emit(ARM_MOV_R(ARM_SP, ARM_FP), ctx);
emit(ARM_POP(CALLEE_POP_MASK), ctx);
#endif
}
......@@ -1422,8 +1388,6 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
emit_rev32(rt, rt, ctx);
goto emit_bswap_uxt;
case 64:
/* Because of the usage of ARM_LR */
ctx->seen |= SEEN_CALL;
emit_rev32(ARM_LR, rt, ctx);
emit_rev32(rt, rd, ctx);
emit(ARM_MOV_R(rd, ARM_LR), ctx);
......
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