From 52fb1756ea1d2759dfef2d86245be00b05dac3a2 Mon Sep 17 00:00:00 2001 From: Pu Lehui Date: Wed, 8 Jul 2026 06:44:33 +0000 Subject: riscv, bpf: Fix kernel stack corruption in tailcall with CFI MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When CONFIG_CFI_CLANG is enabled, prog->bpf_func already skips the kcfi instruction during setup. Including it again in the tailcall jump offset causes it to jump over an extra 4 bytes, skipping the stack pointer adjustment, which will result in kernel stack corruption. Fixes: 30a59cc79754 ("riscv, bpf: Fix possible infinite tailcall when CONFIG_CFI_CLANG is enabled") Reported-by: Sashiko Signed-off-by: Pu Lehui Reviewed-by: Björn Töpel Acked-by: Björn Töpel Link: https://lore.kernel.org/bpf/20260708064436.2971933-5-pulehui@huaweicloud.com Signed-off-by: Kumar Kartikeya Dwivedi --- arch/riscv/net/bpf_jit_comp64.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c index 2f06752fb036..cedf40927474 100644 --- a/arch/riscv/net/bpf_jit_comp64.c +++ b/arch/riscv/net/bpf_jit_comp64.c @@ -18,7 +18,6 @@ #define RV_MAX_REG_ARGS 8 #define RV_FENTRY_NINSNS 2 #define RV_FENTRY_NBYTES (RV_FENTRY_NINSNS * 4) -#define RV_KCFI_NINSNS (IS_ENABLED(CONFIG_CFI) ? 1 : 0) /* imm that allows emit_imm to emit max count insns */ #define RV_MAX_COUNT_IMM 0x7FFF7FF7FF7FF7FF @@ -272,8 +271,8 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx) if (!is_tail_call) emit_addiw(RV_REG_A0, RV_REG_A5, 0, ctx); emit_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA, - /* kcfi, fentry and TCC init insns will be skipped on tailcall */ - is_tail_call ? (RV_KCFI_NINSNS + RV_FENTRY_NINSNS + 1) * 4 : 0, + /* fentry and TCC init insns will be skipped on tailcall */ + is_tail_call ? (RV_FENTRY_NINSNS + 1) * 4 : 0, ctx); } @@ -2033,6 +2032,8 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog) /* emit kcfi type preamble immediately before the first insn */ emit_kcfi(is_subprog ? cfi_bpf_subprog_hash : cfi_bpf_hash, ctx); + /* bpf prog starts here as kcfi skipped during prog->bpf_func setup */ + /* nops reserved for auipc+jalr pair */ for (i = 0; i < RV_FENTRY_NINSNS; i++) emit(rv_nop(), ctx); -- cgit v1.2.3