Re: [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble memory as ROX

On Thu, Jun 1, 2023 at 3:15 AM Mike Rapoport [off-list ref] wrote:

From: Song Liu <song@kernel.org>

Replace direct memory writes to memory allocated for code with text poking
to allow allocation of executable memory as ROX.

The only exception is arch_prepare_bpf_trampoline() that cannot jit
directly into module memory yet, so it uses set_memory calls to
unprotect the memory before writing to it and to protect memory in the
end.

Signed-off-by: Song Liu <song@kernel.org>
Co-developed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
---
 arch/x86/kernel/alternative.c | 43 +++++++++++++++++++++++------------
 arch/x86/kernel/ftrace.c      | 41 +++++++++++++++++++++------------
 arch/x86/kernel/module.c      | 24 +++++--------------
 arch/x86/kernel/static_call.c | 10 ++++----
 arch/x86/kernel/unwind_orc.c  | 13 +++++++----
 arch/x86/net/bpf_jit_comp.c   | 22 +++++++++++++-----

We need the following in this patch (or before this patch).
Otherwise, the system will crash at the VIRTUAL_BUG_ON()
in vmalloc_to_page().

Thanks,
Song

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index bf954d2721c1..4efa8a795ebc 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c

@@ -1084,7 +1084,7 @@ bpf_jit_binary_pack_alloc(unsigned int proglen,

u8 **image_ptr,
                return NULL;
        }

-       *rw_header = kvmalloc(size, GFP_KERNEL);
+       *rw_header = kvzalloc(size, GFP_KERNEL);
        if (!*rw_header) {
                bpf_arch_text_copy(&ro_header->size, &size, sizeof(size));
                bpf_prog_pack_free(ro_header);

@@ -1092,8 +1092,6 @@ bpf_jit_binary_pack_alloc(unsigned int proglen,

u8 **image_ptr,
                return NULL;
        }

-       /* Fill space with illegal/arch-dep instructions. */
-       bpf_fill_ill_insns(*rw_header, size);
        (*rw_header)->size = size;

        hole = min_t(unsigned int, size - (proglen + sizeof(*ro_header)),