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bpf: Allow uprobe program to change context registers

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Currently uprobe (BPF_PROG_TYPE_KPROBE) program can't write to the
context registers data. While this makes sense for kprobe attachments,
for uprobe attachment it might make sense to be able to change user
space registers to alter application execution.

Since uprobe and kprobe programs share the same type (BPF_PROG_TYPE_KPROBE),
we can't deny write access to context during the program load. We need
to check on it during program attachment to see if it's going to be
kprobe or uprobe.

Storing the program's write attempt to context and checking on it
during the attachment.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20250916215301.664963-2-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Jiri Olsa
2025-09-16 23:52:56 +02:00
committed by Alexei Starovoitov
parent 34f033a6c9
commit 7384893d97
3 changed files with 12 additions and 2 deletions
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9
kernel/trace/bpf_trace.c
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@@ -1338,8 +1338,6 @@ static bool kprobe_prog_is_valid_access(int off, int size, enum bpf_access_type
{
if (off < 0 || off >= sizeof(struct pt_regs))
return false;
if (type != BPF_READ)
return false;
if (off % size != 0)
return false;
/*
@@ -1349,6 +1347,9 @@ static bool kprobe_prog_is_valid_access(int off, int size, enum bpf_access_type
if (off + size > sizeof(struct pt_regs))
return false;
if (type == BPF_WRITE)
prog->aux->kprobe_write_ctx = true;
return true;
}
@@ -2735,6 +2736,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
if (!is_kprobe_multi(prog))
return -EINVAL;
/* Writing to context is not allowed for kprobes. */
if (prog->aux->kprobe_write_ctx)
return -EINVAL;
flags = attr->link_create.kprobe_multi.flags;
if (flags & ~BPF_F_KPROBE_MULTI_RETURN)
return -EINVAL;