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Subject[PATCH 4.14 19/71] ARM: net: bpf: fix register saving
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Russell King <rmk+kernel@armlinux.org.uk>

commit 02088d9b392f605c892894b46aa8c83e3abd0115 upstream.

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: 39c13c204bb1 ("arm: eBPF JIT compiler")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm/net/bpf_jit_32.c | 80 ++++++++++++----------------------------------
1 file changed, 22 insertions(+), 58 deletions(-)

--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -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

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, u
}

/* 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(cons
/* 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(con
/* 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(cons
/* 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(cons
/* 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 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_ct
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_ct
/* 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_i
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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