selftests/x86/sigreturn/32: Invalidate DS and ES when abusing the kernel (4d2fa82d) · Commits · 戴 / test

If the kernel accidentally uses DS or ES while the user values are loaded, it will work fine for sane userspace. In the interest of simulating maximally insane userspace, make sigreturn_32 zero out DS and ES for the nasty parts so that inadvertent use of these segments will crash. Signed-off-by:

Andy Lutomirski <luto@kernel.org> Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Cc: stable@kernel.org

tools/testing/selftests/x86/sigreturn.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -451,6 +451,19 @@ static void sigusr1(int sig, siginfo_t info, void ctx_void)
		ctx->uc_mcontext.gregs[REG_SP] = (unsigned long)0x8badf00d5aadc0deULL;
		ctx->uc_mcontext.gregs[REG_CX] = 0;

		#ifdef __i386__
		/*
		* Make sure the kernel doesn't inadvertently use DS or ES-relative
		* accesses in a region where user DS or ES is loaded.
		*
		* Skip this for 64-bit builds because long mode doesn't care about
		* DS and ES and skipping it increases test coverage a little bit,
		* since 64-bit kernels can still run the 32-bit build.
		*/
		ctx->uc_mcontext.gregs[REG_DS] = 0;
		ctx->uc_mcontext.gregs[REG_ES] = 0;
		#endif

		memcpy(&requested_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
		requested_regs[REG_CX] = ssptr(ctx); / The asm code does this. */

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