Commit e63985ec authored by Puranjay Mohan's avatar Puranjay Mohan Committed by Andrii Nakryiko
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bpf, riscv64/cfi: Support kCFI + BPF on riscv64 



The riscv BPF JIT doesn't emit proper kCFI prologues for BPF programs
and struct_ops trampolines when CONFIG_CFI_CLANG is enabled.

This causes CFI failures when calling BPF programs and can even crash
the kernel due to invalid memory accesses.

Example crash:

root@rv-selftester:~/bpf# ./test_progs -a dummy_st_ops

 Unable to handle kernel paging request at virtual address ffffffff78204ffc
 Oops [#1]
 Modules linked in: bpf_testmod(OE) [....]
 CPU: 3 PID: 356 Comm: test_progs Tainted: P           OE      6.8.0-rc1 #1
 Hardware name: riscv-virtio,qemu (DT)
 epc : bpf_struct_ops_test_run+0x28c/0x5fc
  ra : bpf_struct_ops_test_run+0x26c/0x5fc
 epc : ffffffff82958010 ra : ffffffff82957ff0 sp : ff200000007abc80
  gp : ffffffff868d6218 tp : ff6000008d87b840 t0 : 000000000000000f
  t1 : 0000000000000000 t2 : 000000002005793e s0 : ff200000007abcf0
  s1 : ff6000008a90fee0 a0 : 0000000000000000 a1 : 0000000000000000
  a2 : 0000000000000000 a3 : 0000000000000000 a4 : 0000000000000000
  a5 : ffffffff868dba26 a6 : 0000000000000001 a7 : 0000000052464e43
  s2 : 00007ffffc0a95f0 s3 : ff6000008a90fe80 s4 : ff60000084c24c00
  s5 : ffffffff78205000 s6 : ff60000088750648 s7 : ff20000000035008
  s8 : fffffffffffffff4 s9 : ffffffff86200610 s10: 0000000000000000
  s11: 0000000000000000 t3 : ffffffff8483dc30 t4 : ffffffff8483dc10
  t5 : ffffffff8483dbf0 t6 : ffffffff8483dbd0
 status: 0000000200000120 badaddr: ffffffff78204ffc cause: 000000000000000d
 [<ffffffff82958010>] bpf_struct_ops_test_run+0x28c/0x5fc
 [<ffffffff805083ee>] bpf_prog_test_run+0x170/0x548
 [<ffffffff805029c8>] __sys_bpf+0x2d2/0x378
 [<ffffffff804ff570>] __riscv_sys_bpf+0x5c/0x120
 [<ffffffff8000e8fe>] syscall_handler+0x62/0xe4
 [<ffffffff83362df6>] do_trap_ecall_u+0xc6/0x27c
 [<ffffffff833822c4>] ret_from_exception+0x0/0x64
 Code: b603 0109 b683 0189 b703 0209 8493 0609 157d 8d65 (a303) ffca
 ---[ end trace 0000000000000000 ]---
 Kernel panic - not syncing: Fatal exception
 SMP: stopping secondary CPUs

Implement proper kCFI prologues for the BPF programs and callbacks and
drop __nocfi for riscv64. Fix the trampoline generation code to emit kCFI
prologue when a struct_ops trampoline is being prepared.

Signed-off-by: default avatarPuranjay Mohan <puranjay12@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarBjörn Töpel <bjorn@kernel.org>
Link: https://lore.kernel.org/bpf/20240303170207.82201-2-puranjay12@gmail.com
parent 516fca5a

arch/riscv/include/asm/cfi.h

+17 −0
Original line number Diff line number Diff line
@@ -13,11 +13,28 @@ struct pt_regs; 


#ifdef CONFIG_CFI_CLANG

enum bug_trap_type handle_cfi_failure(struct pt_regs *regs);

#define __bpfcall

static inline int cfi_get_offset(void)

{

	return 4;

}



#define cfi_get_offset cfi_get_offset

extern u32 cfi_bpf_hash;

extern u32 cfi_bpf_subprog_hash;

extern u32 cfi_get_func_hash(void *func);

#else

static inline enum bug_trap_type handle_cfi_failure(struct pt_regs *regs)

{

	return BUG_TRAP_TYPE_NONE;

}



#define cfi_bpf_hash 0U

#define cfi_bpf_subprog_hash 0U

static inline u32 cfi_get_func_hash(void *func)

{

	return 0;

}

#endif /* CONFIG_CFI_CLANG */



#endif /* _ASM_RISCV_CFI_H */

arch/riscv/kernel/cfi.c

+53 −0
Original line number Diff line number Diff line
@@ -75,3 +75,56 @@ enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) 


	return report_cfi_failure(regs, regs->epc, &target, type);

}



#ifdef CONFIG_CFI_CLANG

struct bpf_insn;



/* Must match bpf_func_t / DEFINE_BPF_PROG_RUN() */

extern unsigned int __bpf_prog_runX(const void *ctx,

				    const struct bpf_insn *insn);



/*

 * Force a reference to the external symbol so the compiler generates

 * __kcfi_typid.

 */

__ADDRESSABLE(__bpf_prog_runX);



/* u32 __ro_after_init cfi_bpf_hash = __kcfi_typeid___bpf_prog_runX; */

asm (

"	.pushsection	.data..ro_after_init,\"aw\",@progbits	\n"

"	.type	cfi_bpf_hash,@object				\n"

"	.globl	cfi_bpf_hash					\n"

"	.p2align	2, 0x0					\n"

"cfi_bpf_hash:							\n"

"	.word	__kcfi_typeid___bpf_prog_runX			\n"

"	.size	cfi_bpf_hash, 4					\n"

"	.popsection						\n"

);



/* Must match bpf_callback_t */

extern u64 __bpf_callback_fn(u64, u64, u64, u64, u64);



__ADDRESSABLE(__bpf_callback_fn);



/* u32 __ro_after_init cfi_bpf_subprog_hash = __kcfi_typeid___bpf_callback_fn; */

asm (

"	.pushsection	.data..ro_after_init,\"aw\",@progbits	\n"

"	.type	cfi_bpf_subprog_hash,@object			\n"

"	.globl	cfi_bpf_subprog_hash				\n"

"	.p2align	2, 0x0					\n"

"cfi_bpf_subprog_hash:						\n"

"	.word	__kcfi_typeid___bpf_callback_fn			\n"

"	.size	cfi_bpf_subprog_hash, 4				\n"

"	.popsection						\n"

);



u32 cfi_get_func_hash(void *func)

{

	u32 hash;



	if (get_kernel_nofault(hash, func - cfi_get_offset()))

		return 0;



	return hash;

}

#endif

arch/riscv/net/bpf_jit.h

+1 −1
Original line number Diff line number Diff line
@@ -1223,7 +1223,7 @@ static inline void emit_bswap(u8 rd, s32 imm, struct rv_jit_context *ctx) 


#endif /* __riscv_xlen == 64 */



void bpf_jit_build_prologue(struct rv_jit_context *ctx);

void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog);

void bpf_jit_build_epilogue(struct rv_jit_context *ctx);



int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,

arch/riscv/net/bpf_jit_comp32.c

+1 −1
Original line number Diff line number Diff line
@@ -1301,7 +1301,7 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx, 
	return 0;

}



void bpf_jit_build_prologue(struct rv_jit_context *ctx)

void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)

{

	const s8 *fp = bpf2rv32[BPF_REG_FP];

	const s8 *r1 = bpf2rv32[BPF_REG_1];

arch/riscv/net/bpf_jit_comp64.c

+13 −1
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#include <linux/memory.h>

#include <linux/stop_machine.h>

#include <asm/patch.h>

#include <asm/cfi.h>

#include "bpf_jit.h"



#define RV_FENTRY_NINSNS 2
@@ -455,6 +456,12 @@ static int emit_call(u64 addr, bool fixed_addr, struct rv_jit_context *ctx) 
	return emit_jump_and_link(RV_REG_RA, off, fixed_addr, ctx);

}



static inline void emit_kcfi(u32 hash, struct rv_jit_context *ctx)

{

	if (IS_ENABLED(CONFIG_CFI_CLANG))

		emit(hash, ctx);

}



static void emit_atomic(u8 rd, u8 rs, s16 off, s32 imm, bool is64,

			struct rv_jit_context *ctx)

{
@@ -869,6 +876,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, 
		emit_sd(RV_REG_SP, stack_size - 16, RV_REG_FP, ctx);

		emit_addi(RV_REG_FP, RV_REG_SP, stack_size, ctx);

	} else {

		/* emit kcfi hash */

		emit_kcfi(cfi_get_func_hash(func_addr), ctx);

		/* For the trampoline called directly, just handle

		 * the frame of trampoline.

		 */
@@ -1711,7 +1720,7 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx, 
	return 0;

}



void bpf_jit_build_prologue(struct rv_jit_context *ctx)

void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)

{

	int i, stack_adjust = 0, store_offset, bpf_stack_adjust;
@@ -1740,6 +1749,9 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx) 


	store_offset = stack_adjust - 8;



	/* emit kcfi type preamble immediately before the  first insn */

	emit_kcfi(is_subprog ? cfi_bpf_subprog_hash : cfi_bpf_hash, ctx);



	/* nops reserved for auipc+jalr pair */

	for (i = 0; i < RV_FENTRY_NINSNS; i++)

		emit(rv_nop(), ctx);