On 13/11/22 6:47 pm, Christophe Leroy wrote:
Le 10/11/2022 à 19:43, Hari Bathini a écrit :
bpf_arch_text_copy is used to dump JITed binary to RX page, allowing
multiple BPF programs to share the same page. Using patch_instruction
to implement it.
Using patch_instruction() is nice for a quick implementation, but it is
probably suboptimal. Due to the amount of data to be copied, it is worth
Yeah.
a dedicated function that maps a RW copy of the page to be updated then
does the copy at once with memcpy() then unmaps the page.
I will see if I can come up with such implementation for the respin.
Signed-off-by: Hari Bathini <hbathini@xxxxxxxxxxxxx>
---
arch/powerpc/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++++++++++++-
1 file changed, 38 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 43e634126514..7383e0effad2 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -13,9 +13,12 @@
#include <linux/netdevice.h>
#include <linux/filter.h>
#include <linux/if_vlan.h>
-#include <asm/kprobes.h>
+#include <linux/memory.h>
#include <linux/bpf.h>
+#include <asm/kprobes.h>
+#include <asm/code-patching.h>
+
#include "bpf_jit.h"
static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
@@ -23,6 +26,35 @@ static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
memset32(area, BREAKPOINT_INSTRUCTION, size / 4);
}
+/*
+ * Patch 'len' bytes of instructions from opcode to addr, one instruction
+ * at a time. Returns addr on success. ERR_PTR(-EINVAL), otherwise.
+ */
+static void *bpf_patch_instructions(void *addr, void *opcode, size_t len)
+{
+ void *ret = ERR_PTR(-EINVAL);
+ size_t patched = 0;
+ u32 *inst = opcode;
+ u32 *start = addr;
+
+ if (WARN_ON_ONCE(core_kernel_text((unsigned long)addr)))
+ return ret;
+
+ mutex_lock(&text_mutex);
+ while (patched < len) {
+ if (patch_instruction(start++, ppc_inst(*inst)))
+ goto error;
+
+ inst++;
+ patched += 4;
+ }
+
+ ret = addr;
+error:
+ mutex_unlock(&text_mutex);
+ return ret;
+}
+
/* Fix updated addresses (for subprog calls, ldimm64, et al) during extra pass */
static int bpf_jit_fixup_addresses(struct bpf_prog *fp, u32 *image,
struct codegen_context *ctx, u32 *addrs)
@@ -357,3 +389,8 @@ int bpf_add_extable_entry(struct bpf_prog *fp, u32 *image, int pass, struct code
ctx->exentry_idx++;
return 0;
}
+
+void *bpf_arch_text_copy(void *dst, void *src, size_t len)
+{
+ return bpf_patch_instructions(dst, src, len);
+}
I can't see the added value of having two functions when the first one
just calls the second one and is the only user of it. Why not have
implemented bpf_patch_instructions() directly inside bpf_arch_text_copy() ?
By the way, it can be nice to have two functions, but split them
differently, to avoid the goto: etc ....
I also prefer using for loops instead of while loops.
It could have looked like below (untested):
static void *bpf_patch_instructions(void *addr, void *opcode, size_t len)
{
u32 *inst = opcode;
u32 *start = addr;
u32 *end = addr + len;
for (inst = opcode, start = addr; start < end; inst++, start++) {
if (patch_instruction(start, ppc_inst(*inst)))
return ERR_PTR(-EINVAL);
}
return addr;
}
void *bpf_arch_text_copy(void *dst, void *src, size_t len)
{
if (WARN_ON_ONCE(core_kernel_text((unsigned long)dst)))
return ret;
mutex_lock(&text_mutex);
ret = bpf_patch_instructions(dst, src, len);
mutex_unlock(&text_mutex);
return ret;
}
Sure. Will use this.
Thanks
Hari
