Fix ksym buffer overrun on 32 bit platforms

Commit 78074c5 ("info: expose more prog jited info"), which made its
way into v0.17.0, resulted in random runc CI failures when running i386
binary on an amd64 kernel (see [1]).

Apparently [2], the kernel always returns 64-bit pointers, so uint64
(rather than uintptr) should be used for ksyms slice regardless of
the platform to avoid the buffer overrun.

Now, to keep the public API of (*ProgramInfo).JitedKsymAddrs intact,
convert those addresses back to uintptr, as it was done before
commit 78074c5. Except, if the kernel address won't fit into an
uintptr (as it is the case when running i386 binary on an amd64 kernel),
return an empty slice and a false, rather than incorrect addresses.

[1]: opencontainers/runc#4594
[2]: https://github.com/torvalds/linux/blob/2014c95afecee3e76ca4a56956a936e23283f05b/kernel/bpf/syscall.c#L4840-L4846

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

Author: kolyshkin

info.go

@@ -185,7 +185,7 @@ type programJitedInfo struct {
 	// subprograms.
 	//
 	// Available from 4.18.
-	ksyms    []uintptr
+	ksyms    []uint64
 	numKsyms uint32
 
 	// insns holds the JITed machine native instructions of the program,
@@ -344,7 +344,7 @@ func newProgramInfoFromFd(fd *sys.FD) (*ProgramInfo, error) {
 
 	if info.NrJitedKsyms > 0 {
 		pi.jitedInfo.numKsyms = info.NrJitedKsyms
-		pi.jitedInfo.ksyms = make([]uintptr, info.NrJitedKsyms)
+		pi.jitedInfo.ksyms = make([]uint64, info.NrJitedKsyms)
 		info2.JitedKsyms = sys.NewSlicePointer(pi.jitedInfo.ksyms)
 		info2.NrJitedKsyms = info.NrJitedKsyms
 		makeSecondCall = true
@@ -630,8 +630,25 @@ func (pi *ProgramInfo) VerifiedInstructions() (uint32, bool) {
 // programs without subprograms (bpf2bpf calls).
 //
 // The bool return value indicates whether this optional field is available.
+//
+// When a kernel address can't fit into uintptr (which is usually the case when
+// running 32 bit program on a 64 bit kernel), this returns an empty slice and
+// a false.
 func (pi *ProgramInfo) JitedKsymAddrs() ([]uintptr, bool) {
-	return pi.jitedInfo.ksyms, len(pi.jitedInfo.ksyms) > 0
+	ksyms := make([]uintptr, 0, len(pi.jitedInfo.ksyms))
+	if cap(ksyms) == 0 {
+		return ksyms, false
+	}
+	// Check if a kernel address fits into uintptr (it might not when
+	// using a 32 bit binary on a 64 bit kernel). This check should work
+	// with any kernel address, since they have 1s at the highest bits.
+	if a := pi.jitedInfo.ksyms[0]; uint64(uintptr(a)) != a {
+		return nil, false
+	}
+	for _, ksym := range pi.jitedInfo.ksyms {
+		ksyms = append(ksyms, uintptr(ksym))
+	}
+	return ksyms, true
 }
 
 // JitedInsns returns the JITed machine native instructions of the program.