Commit b66a9c9b authored by Paul Chaignon's avatar Paul Chaignon

Detect external pointers from context pointers

The bcc rewriter is currently unable to detect external pointers
(i.e., to a memory address that requires calls to bpf_probe_read) if
they are not declared as arguments, e.g., if they are retrieved
through the context argument.
For example, although the two following examples translate to the
same C code in the end (the bcc rewriter translates the first into
the second), the sk pointer is recognized as an external pointer only
in the first example.

int test1(struct pt_regs *ctx, struct sock *sk) {
    // sk is correctly recognized as an external pointer.
}
int test2(struct pt_regs *ctx) {
    struct sock *sk = (struct sock *)ctx->di;
    // sk is not recognized as an external pointer.
}

This commit fixes that by detecting member dereferences of the
context argument (i.e., the first argument of externally visible
functions). It also works for the TRACEPOINT_PROBE macro.
parent 18c8c141
......@@ -156,9 +156,10 @@ ProbeVisitor::ProbeVisitor(ASTContext &C, Rewriter &rewriter, set<Decl *> &m) :
bool ProbeVisitor::VisitVarDecl(VarDecl *Decl) {
if (Expr *E = Decl->getInit()) {
if (ProbeChecker(E, ptregs_).is_transitive())
if (ProbeChecker(E, ptregs_).is_transitive() || IsContextMemberExpr(E)) {
set_ptreg(Decl);
}
}
return true;
}
bool ProbeVisitor::VisitCallExpr(CallExpr *Call) {
......@@ -185,7 +186,7 @@ bool ProbeVisitor::VisitBinaryOperator(BinaryOperator *E) {
if (ProbeChecker(E->getRHS(), ptregs_).is_transitive()) {
ProbeSetter setter(&ptregs_);
setter.TraverseStmt(E->getLHS());
} else if (E->isAssignmentOp() && E->getRHS()->getStmtClass() == Stmt::CallExprClass) {
} else if (E->getRHS()->getStmtClass() == Stmt::CallExprClass) {
CallExpr *Call = dyn_cast<CallExpr>(E->getRHS());
if (MemberExpr *Memb = dyn_cast<MemberExpr>(Call->getCallee()->IgnoreImplicit())) {
StringRef memb_name = Memb->getMemberDecl()->getName();
......@@ -204,6 +205,9 @@ bool ProbeVisitor::VisitBinaryOperator(BinaryOperator *E) {
}
}
}
} else if (IsContextMemberExpr(E->getRHS())) {
ProbeSetter setter(&ptregs_);
setter.TraverseStmt(E->getLHS());
}
return true;
}
......@@ -262,6 +266,40 @@ bool ProbeVisitor::VisitMemberExpr(MemberExpr *E) {
return true;
}
bool ProbeVisitor::IsContextMemberExpr(Expr *E) {
if (!E->getType()->isPointerType())
return false;
MemberExpr *Memb = dyn_cast<MemberExpr>(E->IgnoreParenCasts());
Expr *base;
SourceLocation rhs_start, member;
bool found = false;
MemberExpr *M;
for (M = Memb; M; M = dyn_cast<MemberExpr>(M->getBase())) {
memb_visited_.insert(M);
rhs_start = M->getLocEnd();
base = M->getBase();
member = M->getMemberLoc();
if (M->isArrow()) {
found = true;
break;
}
}
if (!found) {
return false;
}
if (member.isInvalid()) {
return false;
}
if (DeclRefExpr *base_expr = dyn_cast<DeclRefExpr>(base->IgnoreImplicit())) {
if (base_expr->getDecl() == ctx_) {
return true;
}
}
return false;
}
SourceRange
ProbeVisitor::expansionRange(SourceRange range) {
return rewriter_.getSourceMgr().getExpansionRange(range);
......@@ -862,9 +900,12 @@ void BTypeConsumer::HandleTranslationUnit(ASTContext &Context) {
if (FunctionDecl *F = dyn_cast<FunctionDecl>(D)) {
if (fe_.is_rewritable_ext_func(F)) {
for (auto arg : F->parameters()) {
if (arg != F->getParamDecl(0) && !arg->getType()->isFundamentalType())
if (arg == F->getParamDecl(0)) {
probe_visitor_.set_ctx(arg);
} else if (!arg->getType()->isFundamentalType()) {
probe_visitor_.set_ptreg(arg);
}
}
probe_visitor_.TraverseDecl(D);
}
}
......
......@@ -95,7 +95,9 @@ class ProbeVisitor : public clang::RecursiveASTVisitor<ProbeVisitor> {
bool VisitUnaryOperator(clang::UnaryOperator *E);
bool VisitMemberExpr(clang::MemberExpr *E);
void set_ptreg(clang::Decl *D) { ptregs_.insert(D); }
void set_ctx(clang::Decl *D) { ctx_ = D; }
private:
bool IsContextMemberExpr(clang::Expr *E);
clang::SourceRange expansionRange(clang::SourceRange range);
template <unsigned N>
clang::DiagnosticBuilder error(clang::SourceLocation loc, const char (&fmt)[N]);
......@@ -106,6 +108,7 @@ class ProbeVisitor : public clang::RecursiveASTVisitor<ProbeVisitor> {
std::set<clang::Expr *> memb_visited_;
std::set<clang::Decl *> ptregs_;
std::set<clang::Decl *> &m_;
clang::Decl *ctx_;
};
// A helper class to the frontend action, walks the decls
......
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