summaryrefslogtreecommitdiff
path: root/arch/x86
diff options
context:
space:
mode:
authorDaniel Borkmann <daniel@iogearbox.net>2018-02-22 15:12:53 +0100
committerAlexei Starovoitov <ast@kernel.org>2018-02-22 15:31:42 -0800
commita493a87f38cfa48caaa95c9347be2d914c6fdf29 (patch)
tree326c7205c5ccb29602c6f153fee1ec70924dc5d8 /arch/x86
parent6c5f61023c5b0edb0c8a64c902fe97c6453b1852 (diff)
bpf, x64: implement retpoline for tail call
Implement a retpoline [0] for the BPF tail call JIT'ing that converts the indirect jump via jmp %rax that is used to make the long jump into another JITed BPF image. Since this is subject to speculative execution, we need to control the transient instruction sequence here as well when CONFIG_RETPOLINE is set, and direct it into a pause + lfence loop. The latter aligns also with what gcc / clang emits (e.g. [1]). JIT dump after patch: # bpftool p d x i 1 0: (18) r2 = map[id:1] 2: (b7) r3 = 0 3: (85) call bpf_tail_call#12 4: (b7) r0 = 2 5: (95) exit With CONFIG_RETPOLINE: # bpftool p d j i 1 [...] 33: cmp %edx,0x24(%rsi) 36: jbe 0x0000000000000072 |* 38: mov 0x24(%rbp),%eax 3e: cmp $0x20,%eax 41: ja 0x0000000000000072 | 43: add $0x1,%eax 46: mov %eax,0x24(%rbp) 4c: mov 0x90(%rsi,%rdx,8),%rax 54: test %rax,%rax 57: je 0x0000000000000072 | 59: mov 0x28(%rax),%rax 5d: add $0x25,%rax 61: callq 0x000000000000006d |+ 66: pause | 68: lfence | 6b: jmp 0x0000000000000066 | 6d: mov %rax,(%rsp) | 71: retq | 72: mov $0x2,%eax [...] * relative fall-through jumps in error case + retpoline for indirect jump Without CONFIG_RETPOLINE: # bpftool p d j i 1 [...] 33: cmp %edx,0x24(%rsi) 36: jbe 0x0000000000000063 |* 38: mov 0x24(%rbp),%eax 3e: cmp $0x20,%eax 41: ja 0x0000000000000063 | 43: add $0x1,%eax 46: mov %eax,0x24(%rbp) 4c: mov 0x90(%rsi,%rdx,8),%rax 54: test %rax,%rax 57: je 0x0000000000000063 | 59: mov 0x28(%rax),%rax 5d: add $0x25,%rax 61: jmpq *%rax |- 63: mov $0x2,%eax [...] * relative fall-through jumps in error case - plain indirect jump as before [0] https://support.google.com/faqs/answer/7625886 [1] https://github.com/gcc-mirror/gcc/commit/a31e654fa107be968b802786d747e962c2fcdb2b Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/include/asm/nospec-branch.h37
-rw-r--r--arch/x86/net/bpf_jit_comp.c9
2 files changed, 42 insertions, 4 deletions
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 76b058533e47..81a1be326571 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -177,4 +177,41 @@ static inline void indirect_branch_prediction_barrier(void)
}
#endif /* __ASSEMBLY__ */
+
+/*
+ * Below is used in the eBPF JIT compiler and emits the byte sequence
+ * for the following assembly:
+ *
+ * With retpolines configured:
+ *
+ * callq do_rop
+ * spec_trap:
+ * pause
+ * lfence
+ * jmp spec_trap
+ * do_rop:
+ * mov %rax,(%rsp)
+ * retq
+ *
+ * Without retpolines configured:
+ *
+ * jmp *%rax
+ */
+#ifdef CONFIG_RETPOLINE
+# define RETPOLINE_RAX_BPF_JIT_SIZE 17
+# define RETPOLINE_RAX_BPF_JIT() \
+ EMIT1_off32(0xE8, 7); /* callq do_rop */ \
+ /* spec_trap: */ \
+ EMIT2(0xF3, 0x90); /* pause */ \
+ EMIT3(0x0F, 0xAE, 0xE8); /* lfence */ \
+ EMIT2(0xEB, 0xF9); /* jmp spec_trap */ \
+ /* do_rop: */ \
+ EMIT4(0x48, 0x89, 0x04, 0x24); /* mov %rax,(%rsp) */ \
+ EMIT1(0xC3); /* retq */
+#else
+# define RETPOLINE_RAX_BPF_JIT_SIZE 2
+# define RETPOLINE_RAX_BPF_JIT() \
+ EMIT2(0xFF, 0xE0); /* jmp *%rax */
+#endif
+
#endif /* _ASM_X86_NOSPEC_BRANCH_H_ */
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 4923d92f918d..45e4eb5bcbb2 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -13,6 +13,7 @@
#include <linux/if_vlan.h>
#include <asm/cacheflush.h>
#include <asm/set_memory.h>
+#include <asm/nospec-branch.h>
#include <linux/bpf.h>
/*
@@ -290,7 +291,7 @@ static void emit_bpf_tail_call(u8 **pprog)
EMIT2(0x89, 0xD2); /* mov edx, edx */
EMIT3(0x39, 0x56, /* cmp dword ptr [rsi + 16], edx */
offsetof(struct bpf_array, map.max_entries));
-#define OFFSET1 43 /* number of bytes to jump */
+#define OFFSET1 (41 + RETPOLINE_RAX_BPF_JIT_SIZE) /* number of bytes to jump */
EMIT2(X86_JBE, OFFSET1); /* jbe out */
label1 = cnt;
@@ -299,7 +300,7 @@ static void emit_bpf_tail_call(u8 **pprog)
*/
EMIT2_off32(0x8B, 0x85, 36); /* mov eax, dword ptr [rbp + 36] */
EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT); /* cmp eax, MAX_TAIL_CALL_CNT */
-#define OFFSET2 32
+#define OFFSET2 (30 + RETPOLINE_RAX_BPF_JIT_SIZE)
EMIT2(X86_JA, OFFSET2); /* ja out */
label2 = cnt;
EMIT3(0x83, 0xC0, 0x01); /* add eax, 1 */
@@ -313,7 +314,7 @@ static void emit_bpf_tail_call(u8 **pprog)
* goto out;
*/
EMIT3(0x48, 0x85, 0xC0); /* test rax,rax */
-#define OFFSET3 10
+#define OFFSET3 (8 + RETPOLINE_RAX_BPF_JIT_SIZE)
EMIT2(X86_JE, OFFSET3); /* je out */
label3 = cnt;
@@ -326,7 +327,7 @@ static void emit_bpf_tail_call(u8 **pprog)
* rdi == ctx (1st arg)
* rax == prog->bpf_func + prologue_size
*/
- EMIT2(0xFF, 0xE0); /* jmp rax */
+ RETPOLINE_RAX_BPF_JIT();
/* out: */
BUILD_BUG_ON(cnt - label1 != OFFSET1);