Stable Archive on lore.kernel.org
 help / color / Atom feed
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Piotr Krysiuk <piotras@gmail.com>,
	Benedict Schlueter <benedict.schlueter@rub.de>,
	Daniel Borkmann <daniel@iogearbox.net>,
	John Fastabend <john.fastabend@gmail.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Frank van der Linden <fllinden@amazon.com>
Subject: [PATCH 4.14 34/47] bpf: Tighten speculative pointer arithmetic mask
Date: Tue,  8 Jun 2021 20:27:17 +0200
Message-ID: <20210608175931.597627369@linuxfoundation.org> (raw)
In-Reply-To: <20210608175930.477274100@linuxfoundation.org>

From: Daniel Borkmann <daniel@iogearbox.net>

commit 7fedb63a8307dda0ec3b8969a3b233a1dd7ea8e0 upstream.

This work tightens the offset mask we use for unprivileged pointer arithmetic
in order to mitigate a corner case reported by Piotr and Benedict where in
the speculative domain it is possible to advance, for example, the map value
pointer by up to value_size-1 out-of-bounds in order to leak kernel memory
via side-channel to user space.

Before this change, the computed ptr_limit for retrieve_ptr_limit() helper
represents largest valid distance when moving pointer to the right or left
which is then fed as aux->alu_limit to generate masking instructions against
the offset register. After the change, the derived aux->alu_limit represents
the largest potential value of the offset register which we mask against which
is just a narrower subset of the former limit.

For minimal complexity, we call sanitize_ptr_alu() from 2 observation points
in adjust_ptr_min_max_vals(), that is, before and after the simulated alu
operation. In the first step, we retieve the alu_state and alu_limit before
the operation as well as we branch-off a verifier path and push it to the
verification stack as we did before which checks the dst_reg under truncation,
in other words, when the speculative domain would attempt to move the pointer
out-of-bounds.

In the second step, we retrieve the new alu_limit and calculate the absolute
distance between both. Moreover, we commit the alu_state and final alu_limit
via update_alu_sanitation_state() to the env's instruction aux data, and bail
out from there if there is a mismatch due to coming from different verification
paths with different states.

Reported-by: Piotr Krysiuk <piotras@gmail.com>
Reported-by: Benedict Schlueter <benedict.schlueter@rub.de>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Benedict Schlueter <benedict.schlueter@rub.de>
[fllinden@amazon.com: backported to 4.14]
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/bpf/verifier.c |   70 +++++++++++++++++++++++++++++++-------------------
 1 file changed, 44 insertions(+), 26 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2039,7 +2039,7 @@ static int retrieve_ptr_limit(const stru
 	bool off_is_neg = off_reg->smin_value < 0;
 	bool mask_to_left = (opcode == BPF_ADD &&  off_is_neg) ||
 			    (opcode == BPF_SUB && !off_is_neg);
-	u32 off, max = 0, ptr_limit = 0;
+	u32 max = 0, ptr_limit = 0;
 
 	if (!tnum_is_const(off_reg->var_off) &&
 	    (off_reg->smin_value < 0) != (off_reg->smax_value < 0))
@@ -2048,23 +2048,18 @@ static int retrieve_ptr_limit(const stru
 	switch (ptr_reg->type) {
 	case PTR_TO_STACK:
 		/* Offset 0 is out-of-bounds, but acceptable start for the
-		 * left direction, see BPF_REG_FP.
+		 * left direction, see BPF_REG_FP. Also, unknown scalar
+		 * offset where we would need to deal with min/max bounds is
+		 * currently prohibited for unprivileged.
 		 */
 		max = MAX_BPF_STACK + mask_to_left;
-		off = ptr_reg->off + ptr_reg->var_off.value;
-		if (mask_to_left)
-			ptr_limit = MAX_BPF_STACK + off;
-		else
-			ptr_limit = -off - 1;
+		ptr_limit = -(ptr_reg->var_off.value + ptr_reg->off);
 		break;
 	case PTR_TO_MAP_VALUE:
 		max = ptr_reg->map_ptr->value_size;
-		if (mask_to_left) {
-			ptr_limit = ptr_reg->umax_value + ptr_reg->off;
-		} else {
-			off = ptr_reg->smin_value + ptr_reg->off;
-			ptr_limit = ptr_reg->map_ptr->value_size - off - 1;
-		}
+		ptr_limit = (mask_to_left ?
+			     ptr_reg->smin_value :
+			     ptr_reg->umax_value) + ptr_reg->off;
 		break;
 	default:
 		return REASON_TYPE;
@@ -2119,10 +2114,12 @@ static int sanitize_ptr_alu(struct bpf_v
 			    struct bpf_insn *insn,
 			    const struct bpf_reg_state *ptr_reg,
 			    const struct bpf_reg_state *off_reg,
-			    struct bpf_reg_state *dst_reg)
+			    struct bpf_reg_state *dst_reg,
+			    struct bpf_insn_aux_data *tmp_aux,
+			    const bool commit_window)
 {
+	struct bpf_insn_aux_data *aux = commit_window ? cur_aux(env) : tmp_aux;
 	struct bpf_verifier_state *vstate = env->cur_state;
-	struct bpf_insn_aux_data *aux = cur_aux(env);
 	bool off_is_neg = off_reg->smin_value < 0;
 	bool ptr_is_dst_reg = ptr_reg == dst_reg;
 	u8 opcode = BPF_OP(insn->code);
@@ -2141,18 +2138,33 @@ static int sanitize_ptr_alu(struct bpf_v
 	if (vstate->speculative)
 		goto do_sim;
 
-	alu_state  = off_is_neg ? BPF_ALU_NEG_VALUE : 0;
-	alu_state |= ptr_is_dst_reg ?
-		     BPF_ALU_SANITIZE_SRC : BPF_ALU_SANITIZE_DST;
-
 	err = retrieve_ptr_limit(ptr_reg, off_reg, &alu_limit, opcode);
 	if (err < 0)
 		return err;
 
+	if (commit_window) {
+		/* In commit phase we narrow the masking window based on
+		 * the observed pointer move after the simulated operation.
+		 */
+		alu_state = tmp_aux->alu_state;
+		alu_limit = abs(tmp_aux->alu_limit - alu_limit);
+	} else {
+		alu_state  = off_is_neg ? BPF_ALU_NEG_VALUE : 0;
+		alu_state |= ptr_is_dst_reg ?
+			     BPF_ALU_SANITIZE_SRC : BPF_ALU_SANITIZE_DST;
+	}
+
 	err = update_alu_sanitation_state(aux, alu_state, alu_limit);
 	if (err < 0)
 		return err;
 do_sim:
+	/* If we're in commit phase, we're done here given we already
+	 * pushed the truncated dst_reg into the speculative verification
+	 * stack.
+	 */
+	if (commit_window)
+		return 0;
+
 	/* Simulate and find potential out-of-bounds access under
 	 * speculative execution from truncation as a result of
 	 * masking when off was not within expected range. If off
@@ -2262,6 +2274,7 @@ static int adjust_ptr_min_max_vals(struc
 	    smin_ptr = ptr_reg->smin_value, smax_ptr = ptr_reg->smax_value;
 	u64 umin_val = off_reg->umin_value, umax_val = off_reg->umax_value,
 	    umin_ptr = ptr_reg->umin_value, umax_ptr = ptr_reg->umax_value;
+	struct bpf_insn_aux_data tmp_aux = {};
 	u8 opcode = BPF_OP(insn->code);
 	u32 dst = insn->dst_reg;
 	int ret;
@@ -2314,12 +2327,15 @@ static int adjust_ptr_min_max_vals(struc
 	    !check_reg_sane_offset(env, ptr_reg, ptr_reg->type))
 		return -EINVAL;
 
-	switch (opcode) {
-	case BPF_ADD:
-		ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg);
+	if (sanitize_needed(opcode)) {
+		ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg,
+				       &tmp_aux, false);
 		if (ret < 0)
 			return sanitize_err(env, insn, ret, off_reg, dst_reg);
+	}
 
+	switch (opcode) {
+	case BPF_ADD:
 		/* We can take a fixed offset as long as it doesn't overflow
 		 * the s32 'off' field
 		 */
@@ -2370,10 +2386,6 @@ static int adjust_ptr_min_max_vals(struc
 		}
 		break;
 	case BPF_SUB:
-		ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg);
-		if (ret < 0)
-			return sanitize_err(env, insn, ret, off_reg, dst_reg);
-
 		if (dst_reg == off_reg) {
 			/* scalar -= pointer.  Creates an unknown scalar */
 			if (!env->allow_ptr_leaks)
@@ -2463,6 +2475,12 @@ static int adjust_ptr_min_max_vals(struc
 
 	if (sanitize_check_bounds(env, insn, dst_reg) < 0)
 		return -EACCES;
+	if (sanitize_needed(opcode)) {
+		ret = sanitize_ptr_alu(env, insn, dst_reg, off_reg, dst_reg,
+				       &tmp_aux, true);
+		if (ret < 0)
+			return sanitize_err(env, insn, ret, off_reg, dst_reg);
+	}
 
 	return 0;
 }



  parent reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-08 18:26 [PATCH 4.14 00/47] 4.14.236-rc1 review Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 01/47] net: usb: cdc_ncm: dont spew notifications Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 02/47] efi: Allow EFI_MEMORY_XP and EFI_MEMORY_RO both to be cleared Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 03/47] efi: cper: fix snprintf() use in cper_dimm_err_location() Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 04/47] vfio/pci: Fix error return code in vfio_ecap_init() Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 05/47] vfio/pci: zap_vma_ptes() needs MMU Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 06/47] vfio/platform: fix module_put call in error flow Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 07/47] ipvs: ignore IP_VS_SVC_F_HASHED flag when adding service Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 08/47] HID: pidff: fix error return code in hid_pidff_init() Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 09/47] HID: i2c-hid: fix format string mismatch Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 10/47] netfilter: nfnetlink_cthelper: hit EBUSY on updates if size mismatches Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 11/47] ieee802154: fix error return code in ieee802154_add_iface() Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 12/47] ieee802154: fix error return code in ieee802154_llsec_getparams() Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 13/47] Bluetooth: fix the erroneous flush_work() order Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 14/47] Bluetooth: use correct lock to prevent UAF of hdev object Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 15/47] net: caif: added cfserl_release function Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.14 16/47] net: caif: add proper error handling Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 17/47] net: caif: fix memory leak in caif_device_notify Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 18/47] net: caif: fix memory leak in cfusbl_device_notify Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 19/47] ALSA: timer: Fix master timer notification Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 20/47] ext4: fix bug on in ext4_es_cache_extent as ext4_split_extent_at failed Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 21/47] pid: take a reference when initializing `cad_pid` Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 22/47] ocfs2: fix data corruption by fallocate Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 23/47] nfc: fix NULL ptr dereference in llcp_sock_getname() after failed connect Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 24/47] btrfs: fix error handling in btrfs_del_csums Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 25/47] btrfs: fixup error handling in fixup_inode_link_counts Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 26/47] mm, hugetlb: fix simple resv_huge_pages underflow on UFFDIO_COPY Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 27/47] bpf, selftests: Fix up some test_verifier cases for unprivileged Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 28/47] bpf: Move off_reg into sanitize_ptr_alu Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 29/47] bpf: Ensure off_reg has no mixed signed bounds for all types Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 30/47] bpf: Rework ptr_limit into alu_limit and add common error path Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 31/47] bpf: Improve verifier error messages for users Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 32/47] bpf: Refactor and streamline bounds check into helper Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 33/47] bpf: Move sanitize_val_alu out of op switch Greg Kroah-Hartman
2021-06-08 18:27 ` Greg Kroah-Hartman [this message]
2021-06-08 18:27 ` [PATCH 4.14 35/47] bpf: Update selftests to reflect new error states Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 36/47] bpf: do not allow root to mangle valid pointers Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 37/47] bpf/verifier: disallow pointer subtraction Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 38/47] selftests/bpf: fix test_align Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 39/47] selftests/bpf: make dubious pointer arithmetic test useful Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 40/47] bpf: Fix leakage of uninitialized bpf stack under speculation Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 41/47] bpf: Wrap aux data inside bpf_sanitize_info container Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 42/47] bpf: Fix mask direction swap upon off reg sign change Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 43/47] bpf: No need to simulate speculative domain for immediates Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 44/47] bnxt_en: Remove the setting of dev_port Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 45/47] KVM: SVM: Truncate GPR value for DR and CR accesses in !64-bit mode Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 46/47] sched/fair: Optimize select_idle_cpu Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.14 47/47] xen-pciback: redo VF placement in the virtual topology Greg Kroah-Hartman
2021-06-09  9:33 ` [PATCH 4.14 00/47] 4.14.236-rc1 review Jon Hunter
2021-06-09 11:25 ` Naresh Kamboju
2021-06-09 18:48 ` Guenter Roeck

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210608175931.597627369@linuxfoundation.org \
    --to=gregkh@linuxfoundation.org \
    --cc=ast@kernel.org \
    --cc=benedict.schlueter@rub.de \
    --cc=daniel@iogearbox.net \
    --cc=fllinden@amazon.com \
    --cc=john.fastabend@gmail.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=piotras@gmail.com \
    --cc=stable@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Stable Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/stable/0 stable/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 stable stable/ https://lore.kernel.org/stable \
		stable@vger.kernel.org
	public-inbox-index stable

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.stable


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git