Hi Heiko, Heiko Carstens wrote:
On Wed, Feb 02, 2022 at 12:41:58AM +0100, Ilya Leoshkevich wrote:user_pt_regs is used by eBPF in order to access userspace registers - see commit 466698e654e8 ("s390/bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program type"). In order to access the first syscall argument from eBPF programs, we need to export orig_gpr2. Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx> --- arch/s390/include/asm/ptrace.h | 2 +- arch/s390/include/uapi/asm/ptrace.h | 1 + 2 files changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/s390/include/asm/ptrace.h b/arch/s390/include/asm/ptrace.h index 4ffa8e7f0ed3..c8698e643904 100644 --- a/arch/s390/include/asm/ptrace.h +++ b/arch/s390/include/asm/ptrace.h @@ -83,9 +83,9 @@ struct pt_regs { unsigned long args[1]; psw_t psw; unsigned long gprs[NUM_GPRS]; + unsigned long orig_gpr2; }; }; - unsigned long orig_gpr2; union { struct { unsigned int int_code; diff --git a/arch/s390/include/uapi/asm/ptrace.h b/arch/s390/include/uapi/asm/ptrace.h index ad64d673b5e6..b3dec603f507 100644 --- a/arch/s390/include/uapi/asm/ptrace.h +++ b/arch/s390/include/uapi/asm/ptrace.h @@ -295,6 +295,7 @@ typedef struct { unsigned long args[1]; psw_t psw; unsigned long gprs[NUM_GPRS]; + unsigned long orig_gpr2; } user_pt_regs;Isn't this broken on nearly all architectures? I just checked powerpc, arm64, and riscv. While powerpc seems to mirror pt_regs as user_pt_regs, and therefore exports orig_gpr3, the bpf macros still seem to access the wrong location to access the first syscall parameter(?).
On powerpc, gpr[3] continues to be valid on syscall entry (so this test passes on powerpc), though orig_gpr3 will remain valid throughout.
I will submit a patch to use orig_gpr3 on powerpc. Thanks! - Naveen
