bpf: Introduce bpf register BPF_REG_PARAMS

Introduce BPF_REG_PARAMS as a dedicated BPF register for stack
argument accesses. It occupies the BPF register number 11 (R11),
which is used as the base pointer for the stack argument area,
keeping it separate from the R10-based (BPF_REG_FP) program stack.

The kernel-internal hidden register BPF_REG_AX previously occupied
slot 11 (MAX_BPF_REG). With BPF_REG_PARAMS taking that slot,
BPF_REG_AX moves to slot 12 and MAX_BPF_EXT_REG increases
accordingly.

Acked-by: Puranjay Mohan <puranjay@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260423033506.2542005-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 1ec6d5ba64cc4106eb2f1bc1c40a84a85e79ff52..b77d0b06db6ebce538dc78cb5fded71a841cbfef 100644 (file)
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -58,8 +58,9 @@ struct ctl_table_header;
 #define BPF_REG_H      BPF_REG_9       /* hlen, callee-saved */
 
 /* Kernel hidden auxiliary/helper register. */
-#define BPF_REG_AX             MAX_BPF_REG
-#define MAX_BPF_EXT_REG                (MAX_BPF_REG + 1)
+#define BPF_REG_PARAMS         MAX_BPF_REG
+#define BPF_REG_AX             (MAX_BPF_REG + 1)
+#define MAX_BPF_EXT_REG                (MAX_BPF_REG + 2)
 #define MAX_BPF_JIT_REG                MAX_BPF_EXT_REG
 
 /* unused opcode to mark special call to bpf_tail_call() helper */

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 8b018ff488750b46b64dfea6fee051d81bcaa5d1..ae10b9ca018df5254616864a78a0f8c335c7e77a 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1299,8 +1299,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
        u32 imm_rnd = get_random_u32();
        s16 off;
 
-       BUILD_BUG_ON(BPF_REG_AX  + 1 != MAX_BPF_JIT_REG);
-       BUILD_BUG_ON(MAX_BPF_REG + 1 != MAX_BPF_JIT_REG);
+       BUILD_BUG_ON(BPF_REG_PARAMS + 2 != MAX_BPF_JIT_REG);
+       BUILD_BUG_ON(BPF_REG_AX + 1 != MAX_BPF_JIT_REG);
 
        /* Constraints on AX register:
         *

diff --git a/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c b/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
index 5064aeb8fe670e9409d43e0b1393b2425862a9ea..2c3124092b731bb19ee5373a2478ecb35c148f6b 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
+++ b/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
@@ -69,19 +69,19 @@ static struct test_case test_cases[] = {
 #if defined(__x86_64__) || defined(__aarch64__)
        {
                N(SCHED_CLS, struct __sk_buff, tstamp),
-               .read  = "r11 = *(u8 *)($ctx + sk_buff::__mono_tc_offset);"
-                        "if w11 & 0x4 goto pc+1;"
+               .read  = "r12 = *(u8 *)($ctx + sk_buff::__mono_tc_offset);"
+                        "if w12 & 0x4 goto pc+1;"
                         "goto pc+4;"
-                        "if w11 & 0x3 goto pc+1;"
+                        "if w12 & 0x3 goto pc+1;"
                         "goto pc+2;"
                         "$dst = 0;"
                         "goto pc+1;"
                         "$dst = *(u64 *)($ctx + sk_buff::tstamp);",
-               .write = "r11 = *(u8 *)($ctx + sk_buff::__mono_tc_offset);"
-                        "if w11 & 0x4 goto pc+1;"
+               .write = "r12 = *(u8 *)($ctx + sk_buff::__mono_tc_offset);"
+                        "if w12 & 0x4 goto pc+1;"
                         "goto pc+2;"
-                        "w11 &= -4;"
-                        "*(u8 *)($ctx + sk_buff::__mono_tc_offset) = r11;"
+                        "w12 &= -4;"
+                        "*(u8 *)($ctx + sk_buff::__mono_tc_offset) = r12;"
                         "*(u64 *)($ctx + sk_buff::tstamp) = $src;",
        },
 #endif

diff --git a/tools/testing/selftests/bpf/progs/verifier_bpf_fastcall.c b/tools/testing/selftests/bpf/progs/verifier_bpf_fastcall.c
index fb4fa465d67c62305f6a7d6578647b3aa625a962..0d9e167555b5f2c2c0957ddacbf0dac15610f2bc 100644 (file)
--- a/tools/testing/selftests/bpf/progs/verifier_bpf_fastcall.c
+++ b/tools/testing/selftests/bpf/progs/verifier_bpf_fastcall.c
@@ -630,13 +630,13 @@ __xlated("...")
 __xlated("4: r0 = &(void __percpu *)(r0)")
 __xlated("...")
 /* may_goto expansion starts */
-__xlated("6: r11 = *(u64 *)(r10 -24)")
-__xlated("7: if r11 == 0x0 goto pc+6")
-__xlated("8: r11 -= 1")
-__xlated("9: if r11 != 0x0 goto pc+2")
-__xlated("10: r11 = -24")
+__xlated("6: r12 = *(u64 *)(r10 -24)")
+__xlated("7: if r12 == 0x0 goto pc+6")
+__xlated("8: r12 -= 1")
+__xlated("9: if r12 != 0x0 goto pc+2")
+__xlated("10: r12 = -24")
 __xlated("11: call unknown")
-__xlated("12: *(u64 *)(r10 -24) = r11")
+__xlated("12: *(u64 *)(r10 -24) = r12")
 /* may_goto expansion ends */
 __xlated("13: *(u64 *)(r10 -8) = r1")
 __xlated("14: exit")
@@ -668,13 +668,13 @@ __xlated("1: *(u64 *)(r10 -16) =")
 __xlated("2: r1 = 1")
 __xlated("3: call bpf_get_smp_processor_id")
 /* may_goto expansion starts */
-__xlated("4: r11 = *(u64 *)(r10 -24)")
-__xlated("5: if r11 == 0x0 goto pc+6")
-__xlated("6: r11 -= 1")
-__xlated("7: if r11 != 0x0 goto pc+2")
-__xlated("8: r11 = -24")
+__xlated("4: r12 = *(u64 *)(r10 -24)")
+__xlated("5: if r12 == 0x0 goto pc+6")
+__xlated("6: r12 -= 1")
+__xlated("7: if r12 != 0x0 goto pc+2")
+__xlated("8: r12 = -24")
 __xlated("9: call unknown")
-__xlated("10: *(u64 *)(r10 -24) = r11")
+__xlated("10: *(u64 *)(r10 -24) = r12")
 /* may_goto expansion ends */
 __xlated("11: *(u64 *)(r10 -8) = r1")
 __xlated("12: exit")

diff --git a/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c b/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c
index 6d1edaef92138309d463cf0c8d99c71964abf0e8..4bdf4256a41e512a049047c6379f20a5e07faa96 100644 (file)
--- a/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c
+++ b/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c
@@ -81,13 +81,13 @@ __arch_s390x
 __arch_arm64
 __xlated("0: *(u64 *)(r10 -16) = 65535")
 __xlated("1: *(u64 *)(r10 -8) = 0")
-__xlated("2: r11 = *(u64 *)(r10 -16)")
-__xlated("3: if r11 == 0x0 goto pc+6")
-__xlated("4: r11 -= 1")
-__xlated("5: if r11 != 0x0 goto pc+2")
-__xlated("6: r11 = -16")
+__xlated("2: r12 = *(u64 *)(r10 -16)")
+__xlated("3: if r12 == 0x0 goto pc+6")
+__xlated("4: r12 -= 1")
+__xlated("5: if r12 != 0x0 goto pc+2")
+__xlated("6: r12 = -16")
 __xlated("7: call unknown")
-__xlated("8: *(u64 *)(r10 -16) = r11")
+__xlated("8: *(u64 *)(r10 -16) = r12")
 __xlated("9: r0 = 1")
 __xlated("10: r0 = 2")
 __xlated("11: exit")

diff --git a/tools/testing/selftests/bpf/progs/verifier_sdiv.c b/tools/testing/selftests/bpf/progs/verifier_sdiv.c
index fd59d57e8e3763cb2216f04b98314c2956ef3407..95f3239ce228bd534ef65e652145a88a9af6bf68 100644 (file)
--- a/tools/testing/selftests/bpf/progs/verifier_sdiv.c
+++ b/tools/testing/selftests/bpf/progs/verifier_sdiv.c
@@ -778,10 +778,10 @@ __arch_x86_64
 __xlated("0: r2 = 0x8000000000000000")
 __xlated("2: r3 = -1")
 __xlated("3: r4 = r2")
-__xlated("4: r11 = r3")
-__xlated("5: r11 += 1")
-__xlated("6: if r11 > 0x1 goto pc+4")
-__xlated("7: if r11 == 0x0 goto pc+1")
+__xlated("4: r12 = r3")
+__xlated("5: r12 += 1")
+__xlated("6: if r12 > 0x1 goto pc+4")
+__xlated("7: if r12 == 0x0 goto pc+1")
 __xlated("8: r2 = 0")
 __xlated("9: r2 = -r2")
 __xlated("10: goto pc+1")
@@ -812,10 +812,10 @@ __success __retval(-5)
 __arch_x86_64
 __xlated("0: r2 = 5")
 __xlated("1: r3 = -1")
-__xlated("2: r11 = r3")
-__xlated("3: r11 += 1")
-__xlated("4: if r11 > 0x1 goto pc+4")
-__xlated("5: if r11 == 0x0 goto pc+1")
+__xlated("2: r12 = r3")
+__xlated("3: r12 += 1")
+__xlated("4: if r12 > 0x1 goto pc+4")
+__xlated("5: if r12 == 0x0 goto pc+1")
 __xlated("6: r2 = 0")
 __xlated("7: r2 = -r2")
 __xlated("8: goto pc+1")
@@ -890,10 +890,10 @@ __arch_x86_64
 __xlated("0: w2 = -2147483648")
 __xlated("1: w3 = -1")
 __xlated("2: w4 = w2")
-__xlated("3: r11 = r3")
-__xlated("4: w11 += 1")
-__xlated("5: if w11 > 0x1 goto pc+4")
-__xlated("6: if w11 == 0x0 goto pc+1")
+__xlated("3: r12 = r3")
+__xlated("4: w12 += 1")
+__xlated("5: if w12 > 0x1 goto pc+4")
+__xlated("6: if w12 == 0x0 goto pc+1")
 __xlated("7: w2 = 0")
 __xlated("8: w2 = -w2")
 __xlated("9: goto pc+1")
@@ -925,10 +925,10 @@ __arch_x86_64
 __xlated("0: w2 = -5")
 __xlated("1: w3 = -1")
 __xlated("2: w4 = w2")
-__xlated("3: r11 = r3")
-__xlated("4: w11 += 1")
-__xlated("5: if w11 > 0x1 goto pc+4")
-__xlated("6: if w11 == 0x0 goto pc+1")
+__xlated("3: r12 = r3")
+__xlated("4: w12 += 1")
+__xlated("5: if w12 > 0x1 goto pc+4")
+__xlated("6: if w12 == 0x0 goto pc+1")
 __xlated("7: w2 = 0")
 __xlated("8: w2 = -w2")
 __xlated("9: goto pc+1")
@@ -1004,10 +1004,10 @@ __arch_x86_64
 __xlated("0: r2 = 0x8000000000000000")
 __xlated("2: r3 = -1")
 __xlated("3: r4 = r2")
-__xlated("4: r11 = r3")
-__xlated("5: r11 += 1")
-__xlated("6: if r11 > 0x1 goto pc+3")
-__xlated("7: if r11 == 0x1 goto pc+3")
+__xlated("4: r12 = r3")
+__xlated("5: r12 += 1")
+__xlated("6: if r12 > 0x1 goto pc+3")
+__xlated("7: if r12 == 0x1 goto pc+3")
 __xlated("8: w2 = 0")
 __xlated("9: goto pc+1")
 __xlated("10: r2 s%= r3")
@@ -1034,10 +1034,10 @@ __arch_x86_64
 __xlated("0: r2 = 5")
 __xlated("1: r3 = -1")
 __xlated("2: r4 = r2")
-__xlated("3: r11 = r3")
-__xlated("4: r11 += 1")
-__xlated("5: if r11 > 0x1 goto pc+3")
-__xlated("6: if r11 == 0x1 goto pc+3")
+__xlated("3: r12 = r3")
+__xlated("4: r12 += 1")
+__xlated("5: if r12 > 0x1 goto pc+3")
+__xlated("6: if r12 == 0x1 goto pc+3")
 __xlated("7: w2 = 0")
 __xlated("8: goto pc+1")
 __xlated("9: r2 s%= r3")
@@ -1108,10 +1108,10 @@ __arch_x86_64
 __xlated("0: w2 = -2147483648")
 __xlated("1: w3 = -1")
 __xlated("2: w4 = w2")
-__xlated("3: r11 = r3")
-__xlated("4: w11 += 1")
-__xlated("5: if w11 > 0x1 goto pc+3")
-__xlated("6: if w11 == 0x1 goto pc+4")
+__xlated("3: r12 = r3")
+__xlated("4: w12 += 1")
+__xlated("5: if w12 > 0x1 goto pc+3")
+__xlated("6: if w12 == 0x1 goto pc+4")
 __xlated("7: w2 = 0")
 __xlated("8: goto pc+1")
 __xlated("9: w2 s%= w3")
@@ -1140,10 +1140,10 @@ __arch_x86_64
 __xlated("0: w2 = -5")
 __xlated("1: w3 = -1")
 __xlated("2: w4 = w2")
-__xlated("3: r11 = r3")
-__xlated("4: w11 += 1")
-__xlated("5: if w11 > 0x1 goto pc+3")
-__xlated("6: if w11 == 0x1 goto pc+4")
+__xlated("3: r12 = r3")
+__xlated("4: w12 += 1")
+__xlated("5: if w12 > 0x1 goto pc+3")
+__xlated("6: if w12 == 0x1 goto pc+4")
 __xlated("7: w2 = 0")
 __xlated("8: goto pc+1")
 __xlated("9: w2 s%= w3")