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rseq: Update kernel fields in lockstep with CONFIG_DEBUG_RSEQ=y

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With CONFIG_DEBUG_RSEQ=y, an in-kernel copy of the read-only fields is
kept synchronized with the user-space fields. Ensure the updates are
done in lockstep in case we error out on a write to user-space.

Fixes: 7d5265ffcd ("rseq: Validate read-only fields under DEBUG_RSEQ config")
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/r/20250225202500.731245-1-mjeanson@efficios.com
This commit is contained in:
Michael Jeanson
2025-02-25 15:24:46 -05:00
committed by Ingo Molnar
parent 3c27b40830
commit 79e10dad1c
1 changed files with 41 additions and 41 deletions
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82
kernel/rseq.c
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@@ -78,24 +78,24 @@ efault:
return -EFAULT;
}
static void rseq_set_ro_fields(struct task_struct *t, u32 cpu_id_start, u32 cpu_id,
u32 node_id, u32 mm_cid)
{
rseq_kernel_fields(t)->cpu_id_start = cpu_id;
rseq_kernel_fields(t)->cpu_id = cpu_id;
rseq_kernel_fields(t)->node_id = node_id;
rseq_kernel_fields(t)->mm_cid = mm_cid;
}
/*
* Update an rseq field and its in-kernel copy in lock-step to keep a coherent
* state.
*/
#define rseq_unsafe_put_user(t, value, field, error_label) \
do { \
unsafe_put_user(value, &t->rseq->field, error_label); \
rseq_kernel_fields(t)->field = value; \
} while (0)
#else
static int rseq_validate_ro_fields(struct task_struct *t)
{
return 0;
}
static void rseq_set_ro_fields(struct task_struct *t, u32 cpu_id_start, u32 cpu_id,
u32 node_id, u32 mm_cid)
{
}
#define rseq_unsafe_put_user(t, value, field, error_label) \
unsafe_put_user(value, &t->rseq->field, error_label)
#endif
/*
@@ -173,17 +173,18 @@ static int rseq_update_cpu_node_id(struct task_struct *t)
WARN_ON_ONCE((int) mm_cid < 0);
if (!user_write_access_begin(rseq, t->rseq_len))
goto efault;
unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end);
unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end);
unsafe_put_user(node_id, &rseq->node_id, efault_end);
unsafe_put_user(mm_cid, &rseq->mm_cid, efault_end);
rseq_unsafe_put_user(t, cpu_id, cpu_id_start, efault_end);
rseq_unsafe_put_user(t, cpu_id, cpu_id, efault_end);
rseq_unsafe_put_user(t, node_id, node_id, efault_end);
rseq_unsafe_put_user(t, mm_cid, mm_cid, efault_end);
/*
* Additional feature fields added after ORIG_RSEQ_SIZE
* need to be conditionally updated only if
* t->rseq_len != ORIG_RSEQ_SIZE.
*/
user_write_access_end();
rseq_set_ro_fields(t, cpu_id, cpu_id, node_id, mm_cid);
trace_rseq_update(t);
return 0;
@@ -195,6 +196,7 @@ efault:
static int rseq_reset_rseq_cpu_node_id(struct task_struct *t)
{
struct rseq __user *rseq = t->rseq;
u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED, node_id = 0,
mm_cid = 0;
@@ -202,38 +204,36 @@ static int rseq_reset_rseq_cpu_node_id(struct task_struct *t)
* Validate read-only rseq fields.
*/
if (rseq_validate_ro_fields(t))
return -EFAULT;
/*
* Reset cpu_id_start to its initial state (0).
*/
if (put_user(cpu_id_start, &t->rseq->cpu_id_start))
return -EFAULT;
/*
* Reset cpu_id to RSEQ_CPU_ID_UNINITIALIZED, so any user coming
* in after unregistration can figure out that rseq needs to be
* registered again.
*/
if (put_user(cpu_id, &t->rseq->cpu_id))
return -EFAULT;
/*
* Reset node_id to its initial state (0).
*/
if (put_user(node_id, &t->rseq->node_id))
return -EFAULT;
/*
* Reset mm_cid to its initial state (0).
*/
if (put_user(mm_cid, &t->rseq->mm_cid))
return -EFAULT;
goto efault;
rseq_set_ro_fields(t, cpu_id_start, cpu_id, node_id, mm_cid);
if (!user_write_access_begin(rseq, t->rseq_len))
goto efault;
/*
* Reset all fields to their initial state.
*
* All fields have an initial state of 0 except cpu_id which is set to
* RSEQ_CPU_ID_UNINITIALIZED, so that any user coming in after
* unregistration can figure out that rseq needs to be registered
* again.
*/
rseq_unsafe_put_user(t, cpu_id_start, cpu_id_start, efault_end);
rseq_unsafe_put_user(t, cpu_id, cpu_id, efault_end);
rseq_unsafe_put_user(t, node_id, node_id, efault_end);
rseq_unsafe_put_user(t, mm_cid, mm_cid, efault_end);
/*
* Additional feature fields added after ORIG_RSEQ_SIZE
* need to be conditionally reset only if
* t->rseq_len != ORIG_RSEQ_SIZE.
*/
user_write_access_end();
return 0;
efault_end:
user_write_access_end();
efault:
return -EFAULT;
}
static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)