riscv, bpf: Fix broken BPF tail calls

commit f1003b787c00fbaa4b11619c6b23a885bfce8f07 upstream.

The BPF JIT incorrectly clobbered the a0 register, and did not flag
usage of s5 register when BPF stack was being used.

Fixes: 2353ecc6f91f ("bpf, riscv: add BPF JIT for RV64G")
Signed-off-by: Björn Töpel <bjorn.topel@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191216091343.23260-2-bjorn.topel@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
index 7fbf56a..e2279fe 100644 (file)
--- a/arch/riscv/net/bpf_jit_comp.c
+++ b/arch/riscv/net/bpf_jit_comp.c
@@ -120,6 +120,11 @@ static bool seen_reg(int reg, struct rv_jit_context *ctx)
        return false;
 }
 
+static void mark_fp(struct rv_jit_context *ctx)
+{
+       __set_bit(RV_CTX_F_SEEN_S5, &ctx->flags);
+}
+
 static void mark_call(struct rv_jit_context *ctx)
 {
        __set_bit(RV_CTX_F_SEEN_CALL, &ctx->flags);
@@ -596,7 +601,8 @@ static void __build_epilogue(u8 reg, struct rv_jit_context *ctx)
 
        emit(rv_addi(RV_REG_SP, RV_REG_SP, stack_adjust), ctx);
        /* Set return value. */
-       emit(rv_addi(RV_REG_A0, RV_REG_A5, 0), ctx);
+       if (reg == RV_REG_RA)
+               emit(rv_addi(RV_REG_A0, RV_REG_A5, 0), ctx);
        emit(rv_jalr(RV_REG_ZERO, reg, 0), ctx);
 }
 
@@ -1426,6 +1432,10 @@ static void build_prologue(struct rv_jit_context *ctx)
 {
        int stack_adjust = 0, store_offset, bpf_stack_adjust;
 
+       bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, 16);
+       if (bpf_stack_adjust)
+               mark_fp(ctx);
+
        if (seen_reg(RV_REG_RA, ctx))
                stack_adjust += 8;
        stack_adjust += 8; /* RV_REG_FP */
@@ -1443,7 +1453,6 @@ static void build_prologue(struct rv_jit_context *ctx)
                stack_adjust += 8;
 
        stack_adjust = round_up(stack_adjust, 16);
-       bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, 16);
        stack_adjust += bpf_stack_adjust;
 
        store_offset = stack_adjust - 8;